Airway obstruction during exercise in asthma.

Airway obstruction (AO) in exercise-induced asthma (EIA) is considered a postexercise phenomenon. However, many with EIA complain of respiratory distress during exercise. We evaluated AO in six asthmatic subjects during a short (SX = 6 min) and a long (LX = 20 min) exercise session. We measured peak expiratory flow (PEF) rate, forced expiratory volume in one second (FEV1), and forced expiratory flow at 50% of vital capacity (Vmax50) and calculated expiratory and inspiratory pulmonary resistance (RLe and RLi). Rated perceived exertion (RPE) was evaluated as a measure of dyspnea. All three indices of airflow significantly decreased following SX and LX, but RLi and RLe increased. During SX, PEF, FEV1, and Vmax50 did not decrease, but RLi decreased. During LX, PEF, FEV1, and Vmax50 decreased (20.0, 26.0, and 17.7%, respectively), whereas RLi and RLe significantly increased (74.0 and 53.0%). Rated perceived exertion correlated highly with RLi during exercise (r = 0.95). In summary, there was little or no AO during SX but a frank AO during LX in asthmatic subjects. We conclude that AO occurs during LX and that the manifestation of dyspnea is associated with AO during exercise, as well as in recovery.

Longitudinal effects of aging on lung function at rest and exercise in healthy active fit elderly adults.

We retested 18 healthy, active, and highly fit [maximal O2 consumption (VO2max) 201 +/- 12% of predicted] older adults over a 6-yr period (mean age 67-->73 yr) to determine the longitudinal effects of aging on lung function at rest and during exercise. In the 6-yr period, total lung capacity (TLC), functional residual capacity, and diffusion capacity did not change; vital capacity, forced expiratory volume in 1 s, and maximal volitional flow rates decreased; and residual volume and closing capacity/TLC increased 11-13%, all of which were greater than predicted from cross-sectional data. At maximum exercise over the 6-yr period, VO2max fell 11.2 +/- 3.4% (45.0-->40.3 ml.kg-1.min-1), six (of 18) subjects showed significant arterial hypoxemia (arterial O2 saturation < or = 92%), and maximum heart rate and minute ventilation-to-O2 consumption ratio (VF/VO2) were unchanged. At any given submaximal work rate, VE and breathing frequency were higher, the degree of expiratory flow limitation increased, and end-expiratory and end-inspiratory lung volumes were unchanged but remained significantly higher relative to young adults. We conclude that in contrast to implications from cross-sectional data, our longitudinal findings demonstrate that habitual physical activity and high aerobic capacity modify neither the normal deterioration in resting lung function nor the increased levels of ventilatory work during exercise that occur with healthy aging over the sixth and seventh decades of life.

Static lung load and posture effects on pulmonary mechanics and comfort in underwater exercise.

Static lung load (SLL), or transrespiratory pressure gradient, imposed by underwater breathing apparatus can affect breathing comfort and mechanics, especially during exertion. We examined the effects of body position and SLL on two factors known to affect or limit exertion: a) tidal flow-volume limitation, i.e., the percentage of the tidal volume that meets the boundary of the maximum expiratory flow-volume curve; and b) breathing discomfort. Eight healthy male scuba divers (28 +/- 4 yr) performed cycle ergometry to exhaustion during immersion in each of four combinations of body position and SLL: upright, prone, +10 cmH2O, -10 cmH2O. SLL was referenced to the sternal notch. Tidal flow-volume limitation was significantly greater with the negative SLL (P less than 0.05). In the prone position, higher expiratory flows were achieved (P less than 0.01) and flow limitation was not significantly increased. Respiratory discomfort was quantified with a psychophysical rating scale and increased significantly as exercise intensity increased (P less than 0.01). No effect of posture or SLL on discomfort was found. We conclude that, although respiratory comfort is unaffected, positive static lung loading and the prone body position minimize adverse changes in respiratory mechanics during exercise in immersion.

Flow limitation and regulation of functional residual capacity during exercise in a physically active aging population.

In 29 older (69 +/- 1 yr), physically active subjects (VO2max = 44 +/- 2 ml.kg-1.min-1), we determined the effect of an age-related decline in elastic lung recoil (i.e., Vmax50 = 65% of 30-yr-old adults) on the ventilatory response to progressive exercise. More specifically, we assessed if expiratory airflow limits were achieved and how this may modulate the regulation of end-expiratory lung volume (EELV). We found that with only mild to moderate (50 to 75% VO2max) exercise, the mean EELV was reduced 0.38 +/- 0.07 L, and that expiratory flow limitation was present over 25 +/- 4% of the VT. In 11 subjects during this intensity of exercise, EELV was within their closing capacity. As exercise intensity progressed, VT plateaued at 58 +/- 2% of the vital capacity, and increased expiratory air flow rates were achieved by significantly increasing the EELV back to near resting levels, thereby moving a portion of the expiratory tidal flow-volume envelope away from the constraints of the effort independent portion of the maximal flow-volume curve. During heavy exercise, end-inspiratory lung volume (EILV) approached 90% of TLC. To achieve greater expiratory flow with maximal exercise, EELV remained similar to the previous intensity, and a significantly greater portion of the tidal expiratory flow-volume envelope (greater than 40% of the VT) became flow-limited. Despite this significant expiratory limitation, a rise in EELV, and an EILV approaching TLC, TI/Ttot remained constant throughout exercise, and the ventilatory response for the metabolic demand (VA/VCO2) was appropriate.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical constraints on exercise hyperpnea in a fit aging population.

We studied 12 physically fit (VO2 max = 44 ml.kg-1.min-1) older subjects (age = 63 to 77 yr) who showed the usual age-related declines in lung function (i.e., reduced maximal expiratory flow rates, vital capacity and increased functional residual capacity, closing capacity, and residual volume). We measured the optimal transpulmonary pressures for maximal expiratory airflow and the capacity of the muscles of inspiration for developing pleural pressure (taking into account the effects of lung volume and flow rate). Within these mechanical constraints to ventilation we plotted tidal pleural pressure-volume loops for mild through maximal exercise according to a measured end-expiratory lung volume (EELV). We found EELV to decrease a mean of 0.26 +/- 0.09 L and maximal effective pleural pressures to be reached in nine subjects near EELV with only light to moderate exercise intensities, whereas peak inspiratory pressure was only 45% of the capacity for pressure generation. With progressive increases in exercise intensity, EELV increased, and pleural pressures encroached to a greater extent on the maximal effective pressures; however, they remained effective in the majority of subjects. During maximal exercise EELV was 0.13 +/- 0.10 L greater than resting values, 20% of the Vt reached maximal effective pressures, and 83% of the capacity for inspiratory pressure was achieved. Three subjects significantly surpassed their maximal effective expiratory pressures, and four subjects achieved 95 to 100% of the capacity for inspiratory pressure generation. These subjects also showed no further increase in ventilation while breathing 0.02 to 0.05 FICO2 at maximal exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in frequency of finger tremor in otherwise asymptomatic mercury workers.

Tremor was measured from the index finger during low force, position holding in 18 control subjects and 18 battery workers with low level exposure to mercury. All workers were asymptomatic on clinical neurological examination. No differences were found in average tremor amplitudes between the groups, but statistically significant abnormalities in tremor frequency distribution existed. Tremor power spectra in the group of mercury workers were shifted toward the higher frequencies and compressed into narrow frequency peaks. These results suggest that measurements of finger tremor that evaluate the frequency distribution can produce a higher diagnostic yield than traditional visual clinical judgement. The findings also confirm other reports that currently permitted exposures to mercury are associated with subtle but distinctive differences in tremor accompanying voluntary movement.

Behavioral effects of increased CO2 load in divers.

The behavioral effects of elevated PACO2 were examined to clarify risks due to CO2 retention in diving. In two separate laboratory studies, experienced divers breathed 6% CO2 mixtures under normobaric conditions. Normoxic study: Subjects (n = 8) first breathed air (control); then 6% CO2, 21% O2, balance N2 (exposure); and then air again (postexposure). Hyperoxic study: Subjects (n = 10) first breathed 100% O2; then 6% CO2 in O2; and then O2 again. Subjects performed a test battery in each condition. In the control and postexposure conditions, tests consisted of simple and choice reaction time, postural sway, tremor, and hand steadiness. In the exposure conditions, only the simple and choice reaction time tests were performed. No significant performance decrements during CO2 exposure were found in either study. However, regression analyses indicated that changes in postural sway, tremor, and decision-making time after normoxic CO2 exposure were proportional to decrements in individual end-tidal PCO2 levels following CO2 exposure. We conclude that divers may be at risk for performance impairment immediately after a period of CO2 retention.

Assessment of a cold air breathing aid.

During nasal breathing, heat and humidity are exchanged over a 160 cm(2) area of mucous membrane. This capacity is not sufficient for airway comfort during cold air breathing. Similarly, airway discomfort and constriction may be experienced during exercise-induced mouth breathing in marginally cold temperatures. In asthmatics and sensitive persons such airway discomfort rapidly transforms to broncho-constriction and related breathing problems. The Lungplus mouth-held breathing aid contains a coil of corrugated aluminium foil that provides a heat and moisture exchange area of 1200 cm(2) (Model 1) with a minimal breathing resistance. The present experiment was designed to quantify improved airway comfort using the device. Ninety-one subjects were exposed to each of three rooms with average air temperatures of +20, +3 and -15 degrees C, with a corresponding relative humidity of 50, 70 and 90%. For each condition, subjects gave subjective numerical assessments of the airway sensation during nose, mouth and Lungplus breathing, respectively. At each room temperature, mouth breathing resulted in a less comfortable airway rating than did breathing through the nose, which in turn resulted in a less comfortable rating than the Lungplus breathing condition.

The effects of post-exercise glucose and alanine ingestion on plasma carnitine and ketosis in humans.

1. Several studies have hypothesized that alanine decreases plasma ketone body levels by increasing availability of oxaloacetate, thus allowing acetyl groups to enter the tricarboxylic acid cycle and releasing co-enzyme A (CoA). 2. Four, fasted adult males exercised at 50% of their maximal oxygen consumption for 1.5 h, then ingested 100 g of either glucose or alanine 2 h into recovery. 3. Post-exercise ketosis had developed at 2 h into recovery, as shown by a significantly elevated concentration of beta-hydroxybutyrate in the plasma. At this time plasma free fatty acids were elevated above resting levels while plasma free carnitine concentrations had fallen below resting values. 4. After either alanine or glucose ingestion beta-hydroxybutyrate concentrations fell to the same extent. After the alanine load free carnitine increased above that seen in the glucose trial. Following either alanine or glucose ingestion free fatty acid levels fell; they remained at resting levels in the alanine trial but decreased below rest in the glucose trial. 5. We assume that plasma carnitine concentrations largely reflect the hepatic carnitine pools; therefore, elevations in the plasma free carnitine are probably the result of an increased utilization of acetyl CoA. The significant elevation in plasma free carnitine concentration found after alanine ingestion is consistent with the hypothesis that alanine increases the oxidation of acetyl CoA by providing oxaloacetate for the tricarboxylic acid cycle.

Carnitine metabolism during prolonged exercise and recovery in humans.

Lennon et al. (J. Appl. Physiol. 55: 489-495, 1983) have recently reported a large loss of muscle total carnitine (TC) after 40 min of moderate exercise. These authors have also suggested that elevations in plasma esterified carnitine (EC) were due to the release of these carnitine esters from muscle during exercise. After 10 male subjects underwent 90 min of cycle egometry we found no alteration in muscle TC from preexercise values. Plasma EC progressively increased above resting values during exercise and remained elevated above rest at 0.75 and 1.5 h into recovery. Elevations of plasma EC were largely due to a decrement in free carnitine (FC) in both conditions. Immediately postexercise the urinary fractional reabsorbsion of EC and FC were similar to that at rest. These results suggest that a net loss of TC from exercising muscle does not occur. As in other conditions marked by falling insulin concentrations, elevations in plasma EC could result from an exchange of carnitine with the hepatic carnitine pool.

Physical work capacity in adolescent patients with mild idiopathic scoliosis.

The purpose of this study was to investigate the physical work capacity of adolescent patients with mild idiopathic scoliosis (less than 60 degrees). Fourteen subjects, who were being treated with a Milwaukee brace, were given a progressive exercise stress test. Ventilatory volume, frequency of breathing, end-tidal PCO2, heart rate, and blood pressure were continuously monitored and oxygen consumption (VO2) was computed for each work load. Results indicated that the majority of subjects were 1 to 4 standard deviations above the mean for nonhandicapped peers in expired ventilation, and all of the subjects were 2 standard deviations or more below the mean for their nonhandicapped peers in VO2max. The low work capacity was similar to that reported in individuals with much larger curves. Reduced work capacity was not apparently limited by maximal attainable ventilation or ventilatory pattern (frequency). Reduced aerobic fitness cannot be ruled out.

Chest wall and abdominal motion during exercise in patients with chronic obstructive pulmonary disease.

The study was undertaken to evaluate the role of coordination between the chest wall and abdomen during exercise in patients with chronic obstructive pulmonary disease (COPD). There were 40 patients with COPD and 6 control subjects with normal lung function who underwent a progressive exercise stress test on a treadmill ergometer. The normal subjects exhibited symmetrical motion between the chest wall and abdomen. Three separate patient groups were differentiated by differences in abdominal response to increasing exercise. Group I was similar to normal or showed an early abdominal peak. Group II had a prolonged outward motion of the abdomen, and Group III had an inward motion of the abdomen during inspiration. Resting pulmonary function (FEV1, VC, DL, RV/TLC) and exercise response (duration, O2 saturation, and maximal VO2) were progressively more abnormal from Group I through Group III. The addition of oxygen to Group III had no effect on the pattern observed. However, when 2 patients with a Group III response were reexercised flexed 45 degrees at the waist they no longer were completely paradoxical, they were less dyspneic, and they could walk farther. It is concluded that the chest-abdominal coordination is related to the underlying pulmonary abnormality, and the paradoxical pattern seen in some patients (Group III) is associated with very severe exercise limitation.

Exercise training in patients with COPD.

Exercise is a useful therapeutic intervention for many COPD patients. The progressive stress test is the single most important means of clinical evaluation, although a thorough physical examination and preexercise ECG are also mandatory. The exercise program is prescribed according to duration of exercise and the maximal load reached by the patient during testing. As tolerance builds, exercise time, speed, and grade level are increased. Patients who exercise routinely should be watched carefully for problems, such as hypoxia, hypertension, abnormal right-sided cardiac function, and air tapping. Supplemental oxygen is required for those who are hypoxic.

Acute alterations in stroke volume during exercise at 3,100 m altitude.

Following 3 weeks exposure to an altitude of 3,100 m, the cardiac output response to upright submaximal exercise was examined in 3 healthy subjects breathing ambient air and breathing 60% oxygen. The procedure allowed acute alteration of the 2 conditions within a single testing period of 30 min, 60% oxygen breathing either preceding or following breathing ambient air. Cardiac output was also measured in two of the subjects during maximal exercise under these two conditions. Administration of the high oxygen inspirate during exercise had little effect on the level of cardiac output but resulted in an immediate bradycardia and a dramatic increase of approximately 16% in stroke volume. Stroke volumes during maximal exercise were also increased by approximately 10% by the administration of high oxygen. It is suggested that the condition of decreases exercise stroke volume which develops with chronic exposure to altitude may be largely the result of diminished myocardial contractility stemming from a condition of myocardial hypoxia.