Respiratory gas exchange and physiological demands during a fire fighter evaluation circuit in men and women.

We examined the oxygen uptake (VO2) and carbon dioxide output (VCO2) during completion of a circuit developed for testing fire fighters and related performance time to laboratory measures of fitness. Twenty-two healthy university students (ten women) were trained in the tasks then performed the circuit as quickly as possible. Breath-by-breath gas exchange and heart rate were continuously measured with a portable system. Median circuit time was 6:13 (min:s, 25-75% = 5:46-6:42) for men and 7:25 (25-75% = 6:49-10:21) for 8 women finishers (P = 0.023), and VO2 averaged 68 and 64% VO2max for the men and women during the circuit. Both men and women had high respiratory exchange ratios (>1.0) suggesting marked anaerobic energy contribution. Physiological variables associated with circuit time were assessed by backward stepwise regression yielding a significant model that included only peak work rate during arm cranking exercise as a function of circuit completion time across men and women combined (P < 0.001). For men, but especially for women, the time required for the simulated victim drag (68.2 kg mannequin) was positively correlated with total time to complete the other circuit elements (r = 0.51, r = 0.96 respectively). The simple correlation between circuit time and VO2max (mL/kg/min) revealed poor relationships for men (r = -0.37, P > 0.05) and women (r = 0.20, P > 0.05). These data demonstrated that upper body fitness as reflected by peak work rate during arm cranking correlated with total circuit time for the men and women in our population sample.

Gas exchange, blood lactate, and plasma catecholamines during incremental exercise in hypoxia and normoxia.

The interrelationships among blood lactate (La-) and plasma norepinephrine (NE) and epinephrine (Epi) were studied simultaneously with measures of ventilation (VE) and gas exchange during incremental exercise to exhaustion in nine healthy young men. We wanted to observe whether the tight coupling that exists during normoxic exercise between the concentrations of La- ([La-]) and of both NE and Epi would also be found in hypoxia (inspired O2 fraction = 0.14). In addition, we used recently advocated methods of V slope [CO2 output vs. O2 uptake (VO2)] to select the ventilatory threshold (VT) and log-log transformation of [La-] and VO2 to select the lactate threshold (LT). Peak VO2 was reduced from 4,164 +/- 184 ml/min in normoxia to 3,635 +/- 144 ml/min in hypoxia (P < 0.05). The increase in [La-] was linearly related to the increases in both NE and Epi concentrations in the normoxic and hypoxic tests (r = 0.92-0.96). Estimates of VO2 at VT were significantly greater than those at LT in both normoxia and hypoxia, but these estimates were poorly correlated (r = -0.11-0.46). VT and LT were reduced by hypoxia. Visual interpretation of the VT by examination of VE vs. VO2 and VE/VO2 vs. VO2 did not differ from the LT, but they were less than the VTs by the V-slope method (P < 0.05); yet, all were poorly correlated. The tight coupling between the increase in [La-] and the increase in plasma catecholamines might indicate a common mechanism for the increase or a causative link. VT and LT provided estimates of the general trend in the data, but the poor correlation between them questions the utility of attempting to predict one from the other.

Loads on spinal tissues during simultaneous lifting and ventilatory challenge.

Muscles of the torso have been implicated to play a role in stabilization of the low back, and to assist in ventilation. This motivated an investigation to combine a load challenge to the low back with a breathing challenge, similar to that which a worker might experience when shovelling snow. Perhaps modulation of muscle activity needed to facilitate breathing may compromise the margin of safety of tissues that depend on constant muscle activity for support. Eight young healthy males dynamically lifted, and isometrically held, large loads (73-95 kg) and breathed a 10% CO2 gas mixture to elevate breathing (both with and without hand-held loads). Individual tissue forces were calculated using an anatomically detailed, dynamic model of the torso that was sensitive to individual variation by utilizing myoelectric signals, intra-abdominal pressure, ventilation rate and spine kinematics, obtained from each subject, as input. For large loads in the hands, most subjects appeared to stabilize the trunk with large muscle forces relegating the responsibility of creating lung air flow to the diaphragm. When reasonably small low-back demands were coupled with a breathing challenge and higher ventilation rates two out of eight subjects demonstrated entrainment of abdominal activity to breathing that resulted in additional cyclic low-back compressive loading of the order of 1000 N. Ergonomists should consider the additional tissue loading from physiologically demanding tasks and the related ventilation challenge, together with the tissue loads required to support external objects and maintain body posture.

Cognitive style and personality in 12-year-old children.

Three hundred and eighty 12-year-old children were asked to rate the pupils in their class on seven personality characteristics (Humorous, Shy, Outgoing, Patient, Quiet, Lively, and Serious; part of the sample also rated two additional characteristics, Helpful and Sensible). They were also given the Cognitive Styles Analysis (CSA) (Riding, 1991a) which measures an individual's position on two fundamental cognitive style dimensions; Verbal-Imagery and Wholist-Analytic. A factor analysis indicated that the seven personality characteristics could be viewed as three variables; and these were labelled as Active, Modest and Responsible. Personality characteristic ratings varied significantly as a function of Verbal-Imagery Cognitive Style. Verbalisers were more Active than Imagers, the intermediate position of Bimodal were most Modest and the Imagers were more Responsible than the Verbalisers. There was also a significant gender difference with the girls being more Modest and Responsible and the boys more Active. For the subsample, the only significant effect that was observed related to gender with the girls being rated as more Helpful and more Sensible than the boys.

The early changes in mouse skin following topical application of a range of middle distillate oil products.

A white spirit/naphtha, three kerosines, two gas oils and a catalytically cracked light cycle oil (LCO) were applied topically to mice, three times a week for up to 6 weeks, and skin changes were examined histopathologically at intervals. The changes within 1 week of treatment appeared to depend on the effect that the physicochemical properties of each type of product had on their penetration through the skin surface or via hair follicles. With white spirit the most prominent change was widespread epidermal necrosis occurring after the second treatment, implying that the lowest boiling point materials penetrate mainly through the surface epidermis. The earliest effects with kerosines were within and around hair follicles with epidermal degeneration developing later, suggesting a predominance of follicular entry. Gas oils and LCO produced similar changes to kerosines within 1 week, gas oils producing a slower and less severe response and LCO a more severe response. In skin examined after 1-6 weeks of treatment with all middle distillates, repeated cycles of necrosis and healing responses were evident; this implied that once the epidermal barrier layer had been damaged, follicular entry became less important. The severity of the skin changes observed with these middle distillates was probably sufficient for skin tumours to arise by a non-genotoxic mechanism if a similar treatment regime was used in a long-term skin painting study. A method of avoiding excessive skin irritation is therefore essential in such a study in order to obtain a reliable prediction of the human hazard of such materials.

Role of persistent, non-genotoxic tissue damage in rodent cancer and relevance to humans.

This review has focused on the importance of cellular proliferation in neoplasia induced by nongenotoxic carcinogens and has not attempted to address the mechanisms involved in the progression from the hyperplastic to the neoplastic state. Major advances in this area are likely in the next decade and should explain how cells in an abnormally high proliferative state are rendered more vulnerable either to the action of endogenous or environmental mutagens or to defects in cell reproduction, thus providing the stimulus for progression to neoplasia (165). In this review evidence has been presented to support the hypothesis that sustained tissue damage induced by nongenotoxic compounds in rodents predisposes to tumor development. The evidence has been obtained by drawing from the published findings of experimental rodent studies conducted over the past 50 years. The experience gained at various sites in the rodent including the connective tissue, liver, bladder, and forestomach shows the existence of a threshold dose for various test materials/agents, below which neither sustained tissue damage nor tumor induction occurs but above which level both effects are manifest. Taken collectively, an overall picture emerges that sustained cell proliferation renders various sites in the rodent vulnerable to tumor development. The validity of this hypothesis is of importance to the evaluation of carcinogenic risk of chemicals to humans. For those nongenotoxic carcinogens known to cause characteristically defined and sustainable tissue damage as a precursor of tumor development in rodents, it should be possible to establish a threshold dose below which both effects disappear and upon which a safety margin in humans can be based. Some limited evidence supports an association between chronic tissue injury and neoplastic development in humans. Note, however, that certain types of induced tissue damage may be rodent-specific and therefore have no relevance for humans. We conclude that the appearance of persistent tissue damage predisposes to tumor development in rodents exposed to nongenotoxic carcinogens and that systematic studies in rodents should provide a rational basis for arriving at a safety margin in humans exposed to such agents.

The effect of an abdominal belt on trunk muscle activity and intra-abdominal pressure during squat lifts.

The purpose of this study was to determine whether abdominal belts such as those prescribed to industrial workers reduced trunk muscle activity and/or increased intra-abdominal pressure (IAP). In this study, six subjects lifted loads (72.7 to 90.9 kg) both with and without wearing a weightlifter belt. In addition, further trial conditions required that subjects lifted both with the breath held or continuously expiring on lifting effort. Dynamic hand loads were recorded together with intra-abdominal pressure (IAP) and abdominal, intercostal and low back EMG. Every subject demonstrated an increase in IAP when wearing the belt during both breathing conditions: 99 mmHg with no belt; 120 mmHg wearing belt (p less than 0.0001). However, it was also found that significant increases in IAP occurred (p less than 0.017) when the breath was held versus exhaling with or without the belt. One would expect that if the belt relieved either the direct compressive load on the spine or assisted IAP to produce an extensor moment then this would be reflected in diminished extensor muscle activity. Erector spinae activity tended to be lower with the breath held suggesting a reduced load on the lumbar spine although wearing a belt did not augment this reduction. In the case studies with subjects wearing an ergogenic corset designed for use by industrial manual materials handlers, perceptions of improved trunk stability were reported. However, the muscle activity and IAP results of this study during short duration lifting tasks make it difficult to justify the prescription of abdominal belts to workers.

Relationship between intra-abdominal pressure and trunk EMG.

Intra-abdominal pressure (IAP) has been proposed as an important mechanism in manual lifting and breathing mechanics. Direct (invasive) measures of IAP have required the swallowing of a radio transducer or insertion of a pressure sensor into the rectum or down the oesophagus to the stomach. The purpose of this study was to investigate the relationship between a non-invasive method (EMG) and IAP. Several tasks involving abdominal muscle activation were performed to assess whether or not IAP played a common role in these tasks. IAP and EMG from rectus abdominis, the abdominal obliques, intercostals and erector spinae were measured. Peak IAP reached 340 mmHg (valsalva) for one subject but most values were less than 100 mmHg for tasks other than valsalva. The IAP and EMG data provide some insight into the role of IAP during the performance of specific tasks. Peak IAP within 60 ms of the onset of vigorous abdominal activation indicated the importance of a very rapid pressure response to abdominal muscle activation. The correlations between various muscle EMG time histories and IAP exceeded 0·80 for only two activities (i.e. r(2) = 0·82 between the intercostals and IAP during valsalva manoeuvres). These data suggest that no unifying hypothesis exists to explain the role of IAP for a wide variety of movement tasks; rather, the role of IAP is task specific.

Mechanical and metabolic alterations in rat diaphragm during electrical stimulation.

To investigate the hypothesis that the rate of fatigue development is not influenced by the absolute duration of contraction (train duration) and relaxation (off-phase of duty cycle) at constant duty cycle, strips of the diaphragm from 36 male adult rats (mean +/- SD wt 152 +/- 21 g) were stimulated directly for periods of 180, 250, and 320 ms at a constant duty cycle of 50%. The frequency of stimulation was adjusted to produce 40% of maximal tetanic tension at supramaximal voltages. After 30 min of stimulation, analysis of twitch characteristics between control and experimental groups indicated a prolongation of contraction time of 9% (P less than 0.05), an increase in relaxation time of 75% (P less than 0.05), and a decrease in twitch tension by 78% (P less than 0.05). Similarly, reductions (P less than 0.05) in isometric force output at high stimulation frequency (100 Hz) of 58% and at low frequency (20 Hz) of 67% were also noted. These changes were accompanied by an approximately 60% reduction in the maximal velocity of shortening. No difference was observed for any of the mechanical measures between experimental conditions. After 30-min stimulation, decreases of between 43 and 46% were noted for ATP (P less than 0.05) and increases of between three- and fourfold noted for IMP (P less than 0.05). No changes were found for either ADP or AMP. Total adenine nucleotide concentrations declined (P less than 0.05) an average of 24%. As with the mechanical data, no differences were found between the different stimulation conditions. It is concluded that for the conditions studied, fatigue mechanisms become manifest early in the stimulation period and are only minimally altered by the duration of specific contractions provided the relaxation period is of equal duration.

Capillary and size interrelationships in developing rat diaphragm, EDL, and soleus muscle fiber types.

The effects of maturation on the interrelationship between skeletal muscle fiber area and capillarization was investigated in specific fiber types (I, IIa, IIb, IIc) of male Wistar rats at seven developmental periods ranging from 8 to 85 days postnatal. Fiber type specific developmental properties were compared in three different muscles, the diaphragm (DIA), extensor digitorum longus (EDL), and soleus (SOL), which are known to differ widely in function. All fiber types in each of the three muscles examined exhibited large increases in area (FA), the magnitude and time course of the increase being related to both the type of fiber and the muscle in which the fiber was located. For type I fibers, areas increased from 3- to 18-fold (SOL greater than EDL greater than DIA), whereas in type IIa fibers, area increased ranged between 5- to 11-fold (SOL greater than EDL greater than DIA). Growth rates in IIb fibers were more homogeneous between muscles ranging from 11- to 14-fold. Capillarization, as indicated by the capillary contacts per fiber (CC), increased in all fiber types regardless of muscle origin. These increases ranged between 1.7- and 2.2-fold for type I fibers, between 2.4- and 2.5-fold for type IIa fibers, and between 2.0- and 3.0-fold for type IIb fibers. In general, capillary density expressed as the ratio of the number of capillary contacts divided by the fiber area (CC/FA) progressively declined in all fiber types with age. The rate of the decline in CC/FA was mediated in large part by the changes in fiber area.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessing risks from data on other exposure routes. Possibilities and limitations of using toxicity data derived from one exposure route in assessing risks from other exposure routes.

There is no simple and generally applicable way in which toxicity data derived from one route of exposure can be used to evaluate the effects of exposure by another route in the same species of animal or for risk assessment of another exposure route in man. Reliable predictions may be made in some cases where substances act systemically and have relatively long half-lives and where there are adequate data on toxicity by one route and on pharmacokinetics and metabolism by both routes. Extrapolation may also be possible where it can be shown that the nature and degree of toxicity are directly related to blood or tissue concentrations. The occurrence of toxic effects at the point of exposure (local toxicity) increases the uncertainties associated with extrapolation, usually making it not feasible. The use of safety factors to allow for uncertainties inherent in extrapolating between routes of exposure where data are inadequate is not advocated. Whether an extrapolation of data is justified in an individual case should be decided on a case-by-case basis; generalizations cannot be made.

Early changes produced in mouse skin by the application of three middle distillates.

It has been reported by the American Petroleum Institute (API) that dermal applications of certain middle distillates of mineral oils can result in high incidences of skin tumours in mice. This was unexpected as the polycyclic aromatic hydrocarbon (PAH) levels in these were below detection limits. To examine the possible role of tissue injury in the induction of tumours, the skin reactions produced by thrice weekly applications of three middle distillates similar to those tested by the API were examined grossly and histopathologically at intervals up to 6 weeks. Various reference materials and oils were used as controls. Preliminary histological examination showed that severe skin damage was present from week 1 onwards in mice treated with the three middle distillates, two of them producing epidermal loss and ulceration. Marked epidermal hyperplasia was produced by all three middle distillates. These findings support the view that regenerative epidermal hyperplasia due to repeated severe skin damage may have exerted a powerful promotional effect in the production of the skin tumours by middle distillates in the API study.

Oxidative potential in developing rat diaphragm, EDL, and soleus muscle fibers.

To examine the effect of postnatal development on changes in oxidative potential of fibers of specific types (I, IIa, IIb, and IIc) in the rat diaphragm, determinations of succinate dehydrogenase (SDH) activity were made using microphotometric measures of optical density. Samples of the costal region of the diaphragm were extracted from 56 male Wistar rats ranging in age from 8 to 85 days and subgrouped into seven developmental periods (1, 2, 3, 4, 6, 9, and 12 wk). For type I fibers, increases of 17% (P less than 0.05) in SDH activity occurred during 2nd wk, remained elevated through 4th wk, and increased further (P less than 0.05) to 137% of 1-wk values by the end of 6th wk. No further increases were noted between 6 and 12 wk. A similar maturational trend was evident for type IIa fibers, although SDH activities remained higher throughout development when compared with type I fibers. In contrast, SDH in type IIb fibers, although increasing by 14% during the first two measurement weeks (P less than 0.05), declined from 6 to 9 wk before ultimately reaching a value similar to 3 wk. SDH activity was also assessed in a typical slow- (soleus) and fast-twitch (extensor digitorum longus, EDL) muscle of the hindlimb to contrast their development with that of the diaphragm. Generally, SDH in type I and IIa fibers was approximately 40 and 20% higher, respectively, in the diaphragm than in matched fiber types in the other muscles throughout development (diaphragm greater than EDL greater than soleus).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of end-expiratory lung volume during exercise.

We determined the effects of exercise on active expiration and end-expiratory lung volume (EELV) during steady-state exercise in 13 healthy subjects. We also addressed the questions of what affects active expiration during exercise. Exercise effects on EELV were determined by a He-dilution technique and verified by changes in end-expiratory esophageal pressure. We also used abdominal pressure-volume loops to determine active expiration. EELV was reduced with increasing exercise intensity. EELV was reduced significantly during even mild steady-state exercise and during heavy exercise decreased an average of 0.71 +/- 0.3 liter. Dynamic lung compliance was reduced 30-50%; EELV remained greater than closing volume. Changing the resistance to airflow (via SF6-O2 or He-O2 breathing) during steady-state exercise changed the peak gastric and esophageal pressure generation during expiration but did not alter EELV; breathing through the mouthpiece produced similar effects during exercise. EELV was significantly reduced in the supine position. With supine exercise active expiration was not elicited, and EELV remained the same as in supine rest. With CO2-driven hyperpnea (7-70 l/min), EELV remained unchanged from resting levels, whereas during exercise, at similar minute ventilation (VE) values EELV was consistently decreased. At the same VE, treadmill running caused an increase in tonic gastric pressure and greater reductions in EELV than either walking or cycling. We conclude that both the exercise stimulus and the resultant hyperpnea stimulate active expiration and a reduced FRC. This new EELV is preserved in the face of moderate changes in mechanical time constants of the lung. This reduced EELV during exercise aids inspiration by optimizing diaphragmatic length and permitting elastic recoil of the chest wall.

Exercise-induced changes in functional residual capacity.

We used a helium-rebreathe technique in nine healthy subjects to determine the effects of exercise intensity and duration on end-expiratory lung volume (EELV). The rebreathe functional residual capacity (FRC) technique was shown: (a) to be similar to that measured in the body plethysmograph, at rest; (b) to agree closely with volitionally induced changes in EELV as determined by inductance plethysmography, at rest; (c) to be reproducible within subjects between trials conducted at rest or exercise on different days (r = 0.96, coefficient of variation +/- 3%); (d) to correlate significantly with coincident changes in end-expiratory esophageal pressure from rest to exercise, with increasing exercise intensity and over time at a constant exercise load. Exercise-induced reductions in EELV occurred in all subjects, averaging 0.3 L (-0.1 to -0.7 L) in light exercise and 0.79 L (-0.5 to -1.2 L) in heavy or maximum exercise. This reduction in EELV accounted for slightly more than one-half of the increase in VT during light exercise and slightly less than one-half of the increased VT in heavy exercise. In heavy prolonged exercise lasting 8-15 min, EELV fell in the initial 2 min and was either sustained at this reduced level or fell further with exercise duration to exhaustion. We found that FRC was reduced even in very light exercise when changes in TE and VE from rest were minimal; further reductions in EELV occurred as end-inspiratory lung volume increased and expiratory time shortened with increasing exercise intensity and duration. Based on these types of changes we speculate that active expiration during exercise in humans may be controlled by a combination of locomotor-related feed-forward and lung volume related feed-back mechanisms.

Supramaximal exercise after training-induced hypervolemia. I. Gas exchange and acid-base balance.

The effect of an exercise-induced reduction in blood O2-carrying capacity on ventilatory gas exchange and acid-base balance during supramaximal exercise was studied in six males [peak O2 consumption (VO2peak), 3.98 +/- 0.49 l/min]. Three consecutive days of supramaximal exercise resulted in a preexercise reduction of hemoglobin concentration from 15.8 to 14.0 g/dl (P less than 0.05). During exercise (120% VO2peak) performed intermittently (1 min work to 4 min rest); a small but significant (P less than 0.05) increase was found for both O2 consumption (VO2) (l X min) and heart rate (beats/min) on day 2 of the training. On day 3, VO2 (l/min) was reduced 3.2% (P less than 0.05) over day 1 values. No changes were found in CO2 output and minute ventilation during exercise between training days. Similarly, short-term training failed to significantly alter the changes in arterialized blood PCO2, pH, and [HCO-3] observed during exercise. It is concluded that hypervolemia-induced reductions in O2-carrying capacity in the order of 10-11% cause minimal impairment to gas exchange and acid-base balance during supramaximal non-steady-state exercise.

A physiological profile of elite Canadian freestyle wrestlers.

There has been an improvement in Canadian freestyle wrestling performance over the past five years. Medals are now being won at World and Olympic competitions. The present investigation provides baseline physiological data which have been used in the prescription of individual training programs for these athletes. This information is also available to the coaches and contributes to the strategy for individual matches. Generally, the Canadian wrestlers have a physiological profile similar to elite wrestlers from other countries. Maximal aerobic power is comparable to or greater than previously reported values. Needle biopsies reveal exceptionally large fast twitch fibre areas in vastus lateralis. However, anaerobic capacity and upper body strength are less than values reported for other elite athletes.