Adjustments in oxygen transport during head-out immersion in water at different temperatures.

Respiratory gas exchange was investigated in human subjects immersed up to the shoulders in water at different temperatures (Tw = 25, 34, and 40 degrees C). Cardiac output (Qc) and pulmonary tissue volume (Vti) were measured by a rebreathing technique with the inert gas Freon 22, and O2 consumption (VO2) was determined by the closed-circuit technique. Arterial blood gases (PaO2, PaCO2) were analyzed by a micromethod, and alveolar gas (PAO2) was analyzed during quiet breathing with a mass spectrometer. The findings were as follows. 1) Immersion in a cold bath had no significant effect on Qc compared with the value measured at Tw = 34 degrees C, whereas immersion in a hot bath led to a considerable increase in Qc. Vti was not affected by immersion at any of the temperatures tested. 2) A large rise in metabolic rate VO2 was only observed at Tw = 25 degrees C (P less than 0.001). 3) Arterial blood gases were not significantly affected by immersion, whatever the water temperature. 4) O2 transport during immersion is affected by two main factors: hydrostatic pressure and temperature. Above neutral temperature, O2 transport is improved because of the marked increase in Qc resulting from the combined actions of hydrostatic counter pressure and body heating. Below neutral temperature, O2 transport is altered; an increase in O2 extraction of the tissue is even calculated.

EMG study of respiratory muscles in humans immersed at different water temperatures.

The electromyograms of the rectus abdominis (EMGra) and of the diaphragm (EMGdi) have been recorded on human subjects immersed at two bath temperatures (TW), 25 and 40 degrees C. The recordings were obtained during a calibrated isometric contraction sustained for 20 s against a closed stopcock at functional residual capacity (FRC) level for EMGra (expiratory effort) and at pulmonary volume greater than 90% vital capacity for EMGdi and EMGra (inspiratory effort). After eliminating the electrocardiographic artifact, the EMG signal was processed to obtain its root-mean-square (rms) value and three parameters of its frequency spectrum, total energy (Etot), centroid frequency (fc), and high-to-low ratio (H/L). The results show that EMGdi is not modified by TW. On the other hand rms and Etot of EMGra are always increased at TW = 25 degrees C compared with TW = 40 degrees C, whereas fc and H/L decrease with temperature during the expiratory effort at FRC level but do not vary during inspiratory effort at high pulmonary volume. These results, compared with those previously published for cooled limb muscles, show that TW can elicit EMG alterations on the superficial respiratory muscles through two mechanisms, an intrinsic mechanism due to the local variation in muscle temperature and an extrinsic mechanism acting upon the control system of the muscle contraction. Linked alterations of the muscular mechanical activity probably account for the observed effects of TW on the statics and the dynamics of the pulmonary volumes.

Solubility of Freon 22 in human blood and lung tissue.

The solubility of Freon 22 in human blood and lung tissue was determined using the chromatographic method of Wagner et al. (J. Appl. Physiol. 36: 600-605, 1974). In normal human blood, the mean Bunsen coefficient of solubility (alpha B) was 0.804 cm3 STPD.cm-3.ATA-1 at 37 degrees C. It increased with hematocrit (Hct) according to the equation alpha B = 0.274 Hct + 0.691. Tissue homogenates were prepared from macroscopically normal lung pieces obtained at thoracotomy from eight patients undergoing resection for lung carcinoma. The Bunsen solubility coefficients were 0.537 +/- 0.068 and 0.635 +/- 0.091 in washed and unwashed lung, respectively. These values can be used in the determination of both cardiac output and pulmonary tissue volume in humans by use of the rebreathing technique.

Effects of water temperature on pulmonary volumes in immersed human subjects.

Pulmonary volumes and capacities have been measured at three water temperatures (Tw = 25, 34, 40 degrees C) in standing subjects immersed up to the shoulders. The comparison of data obtained in air with those obtained in thermoneutral immersion (Tw = 34 degrees C) confirms the results previously published in several studies. The comparison of data obtained in immersion at different Tw shows: 1. A significant decrease in vital capacity (VC) with bath temperature (VC 40 degrees C greater than VC 34 degrees C greater than VC 25 degrees C). The same decrease is observed in the inspiratory reserve volume (IRV) while the expiratory reserve volume (ERV), the residual volume (RV) and the functional residual capacity (FRC) do not vary. 2. A significant decrease in maximum breathing capacity (MBC) with bath temperature (MBC 40 degrees C greater than MBC 25 degrees C). 3. A significant increase in tidal volume (VT) in cold or hot water compared to thermoneutral water (VT40 degrees C greater than VT34 degrees C; VT34 degrees C less than VT25 degrees C) during quiet breathing. Breathing frequency does not change, thus ventilation (V) follows the same evolution as VT. The relative abdominal (ABD) contribution to VT, estimated by a double belt inductance plethysmograph, is reduced at Tw = 25 degrees C but unchanged at Tw = 40 degrees C compared to thermoneutral bath. Beside variations in the metabolic state, the variations of the pulmonary volumes as a function of Tw are estimated to be mainly due to alterations in respiratory muscles functioning.

A graphic analysis of respiratory heat exchange.

A new graphic representation of respiratory heat exchange is proposed using the concept of equivalent temperatures directly related to enthalpy values. On such a diagram it is possible to 1) compute the value of the heat exchange (delta H) knowing the inspired temperature (TI) and the partial pressure of water vapor (PIH2O) [or the relative humidity (rhI)] of inspired gas; 2) estimate the variation in delta H following a given variation in TI and PIH2O or, inversely, to choose the variation in TI and PIH2O necessary to obtain a given variation in delta H; 3) dissociate inspiratory and expiratory exchanges and to evaluate the efficiency of the respiratory heat exchange process in different environmental situations; and 4) easily compare the results of different studies published on respiratory heat exchanges in humans or other animal species.

Heat and water respiratory exchanges: comparison between mouth and nose breathing in humans.

The temperatures (TI, TE) of inspired and expired gas and the mass of expired water (MEH2O) have been measured in four subjects at rest during mouth and nose breathing of dry air at room temperature. TI and TE were measured by copper-constantan thermocouples, MEH2O by freezing and ventilatory parameters by total body plethysmography. During mouth breathing, temperatures are significantly higher (TI = 28.1 degrees C, TE = 31.5 degrees C) and the amount of expired water larger (MEH2O = 27.8 mg dm-3 BTPS) than during nose breathing (TI = 24.8 degrees C; TE = 29.6 degrees C; MEH2O = 26.6 mg dm-3 BTPS). From these experimental data the appropriate computations show clearly that in humans, while either nose or mouth breathing, the expired air is not water saturated; the latent heat exchanges represent the larger part of the respiratory heat exchanges; the counter current expiratory heat recovery is imperfect; in terms of heat and water respiratory exchanges, no large difference exists between the oral and nasal routes. This last point is confirmed by the calculation of a difference less than 10% in the total respiratory heat losses between mouth and nose breathing.

Computation of respiratory heat exchanges.

Two sets of equations have been proposed to estimate the convective or sensible (WCV) and the evaporative or insensible (WEV) respiratory heat exchanges. They are applicable both at sea-level barometric pressure with air breathing (SLA) and in hypo- or hyperbaria in both air (HA) and artificial (HAA) atmospheres. The only environmental parameters required are in SLA: the temperature (TI) and the partial pressure of water vapor of the inspired air (PIH2O); in HA: TI, PIH2O, and the actual barometric pressure (PB); and in HAA: IT, PIH2O, PB, the volumetric mass (rho mix), and the specific heat (cp mix) of the breathed gas mixture. When no physiological data are available the results are expressed in energy units per liter of pulmonary ventilation (WCV/V and WEV/V) in J X dm-3 BTPS. If the ventilation value (V) is known the results are obtained in units of power (W).

Postprandial thermogenesis and hormonal release in lean and obese subjects.

One group of 10 obese people (1.72 times normal weight) was compared to a control group of 9 normal-weight subjects. Oxygen consumption (VO2), immuno reactive growth hormone (IRGH), and rectal temperature (Tre) were measured every 15 min on an average, during the 5 h following a protein meal composed of 6 egg-whites and 50 g of casein totaling 1 340 kJ. The results show that postprandial thermogenesis (PPT) is the same in both groups: maximum increase in VO2 averages 15% in the obese and 16% in the control groups respectively. Energy expenditure integrated over the 5 h was 129 kJ for the obese and 114 kJ for the control subjects, i.e. 9.6% and 8.5% of the energy meal content. The rise in Tre was identical for both groups (0.4 degrees C over 3 h). For IRGH, the preprandial reference figures were much lower in the obese: 52 pmole.dm-3, as compared to 145 pmole.dm-3. In all control subjects, the protein meal resulted in a IRGH peak of, on average, 455 pmole.dm-3 about 2 h after. This was not observed in 4 of the obese subjects, while in the remaining 6, the mean peak value was 165 pmole.dm-3, occurring after 1 h. The other hormonal or chemical compound simultaneously analysed (glucagon, cortisol, PRL, T3, glucose, lactate, NEFA) do not show any significant variations but insulin blood level for which a postprandial increase was measured in both groups. It is concluded that after a protein test meal: PPT in overweight people is no different from that in people of normal weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Analytical simulation of longitudinal gas mixing in the human central airways.

In order to study gaseous mixing in the proximal respiratory airways during stationary breathing, a simple mathematical model with an analytical solution of the corresponding equation is presented. Calculations were carried out by solving the differential equation analytically according to the system response to a unit impulse combined with the convolution method. It seems that this analytical method gives similar results to those obtained by the numerical ones; however, our method is computationally simple and can provide a reasonable tool to study gas transport in the airways.

Respiratory water loss as a function of ventilatory or environmental factors.

Since expired gas is not water-saturated (Ferrus et al., 1980, Respir. Physiol. 39: 367-381), its water content should depend on biological or environmental factors other than expired gas temperature. In order to verify this hypothesis, multiple linear regression relationships between MEH2O, the mass of water expired per litre of BTPS ventilated gas and respiratory frequency (f) or period (TR), tidal volume (VT), ventilation (V), temperature of inspired gas (TI), density of inspired gas mixture (rho I), partial pressure of water in inspired gas (PIH2O) were computed from 345 experiments performed on 7 subjects. This analysis shows that MEH2O is positively and significantly correlated to TI (0.22 mg . dm-3 . degrees C-1), to PIH2O (0.14 mg . dm-3 . Torr-1), and to TR (0.87 mg . dm3 . s-1). MEH2O is negatively and significantly correlated to f (-0.27 mg . dm-3(cy . min-1)-1) to rho I (-0.06 mg . dm-3(g . dm-3)-1) and to V (-0.09 mg . dm-3(dm3 . min-1)-1). There is no statistical correlation between MEH2O and VT. It is concluded that the respiratory water loss depends to a large degree on respiratory or environmental conditions. This dependence supports the previously published results suggesting that expired gas is not water saturated.

Determinants of increased energy cost of submaximal exercise in obese subjects.

The energy cost of submaximal cycling exercises is studied in 23 obese (OS) and 13 lean control (LS) subjects at 1) a constant pedaling frequency (60 rpm) and at various work loads [external work loads (Wmec) up to 100 W] for one group of OS and LS, and at 2) constant Wmec (brake free and 60 or 70 W) and various frequencies (38-70 rpm) for a second group of OS and LS. The total energy expenditure (WO2) is calculated from O2 consumption (VO2) measured in both conditions and is compared with anthropometric data. The results show that at rest or at the same Wmec, WO2 is always greater in OS than in LS. At rest the quotients of WO2 over body surface area are not significantly different. At work the difference in WO2 cannot be explained by the muscular mechanical efficiency, which is not statistically different in OS (26 +/- 7.8%) and LS (25 +/- 4.6%). The calculated increase in the work of breathing of OS can account only for 5-15% of the energy overexpenditure. The energy cost of leg movement is estimated in brake-free cycling trials; it is significantly greater in OS than in LS (118 J compared with 68 J/pedal stroke), but when divided by leg volume the figures are not different (9.2 compared with 8.5 J X dm-3 X pedal stroke-1). Leg moving may account for approximately 60-70% of the energy cost of moderate exercise in cycling OS. The remaining difference in WO2 between OS and LS (20-30%) may be explained by an increase in muscular postural activity related to the lack of physical training of OS.

Pulmonary capillary blood volume during immersion in water at different temperatures.

Pulmonary capillary blood volume (Qc) was determined for 7 subjects in the standing posture and immersed up to the sternal manubrium at three water temperatures: 34 degrees C +/- 0.5 degrees C, thermally neutral bath; 25 degrees C +/- 0.5 degrees C, cold bath; and 40 degrees C +/- 0.5 degrees C, hot bath. The Qc was calculated from the lung transfer factor DLco measured while breathing two gas mixtures (21.1% O2 and 90.0% O2) during breath holding. Control experiments in a dry air environment show that Qc values for standing posture decrease compared to the sitting values, owing to a redistribution of the intrathoracic blood volume to lower body parts as a result of gravity. Immersion at 34 degrees C in an upright position produces a significant increase in Qc (P less than 0.01). This is a result of the hydrostatic counterpressure: blood shifts from the periphery to the intrathoracic regions. Immersion at 25 degrees C increases Qc compared to the values obtained at 34 degrees C, but the difference is not significant. The contribution of vasoconstriction to blood volume shift in cold water is probably less important than that of hydrostatic counterpressure. During immersion at 40 degrees C, the rise in Qc is very significant (P less than 0.05). This may be explained by an increase in cardiac output and central blood volume when skin temperature is raised at 40 degrees C.

[Respiratory thermal exchanges in man as a function of inspired gas temperature]. / Les échanges thermiques respiratoires chez l'homme en fonction de la température de gaz inspiré.

1. Measurements of respiratory water vapor loses (MEH20) and of respiratory evaporative (WEV) and convective (WCV) heat losses were made on four of five subjects at three levels of inspired gas temperatures (T1): 10 degrees C, 22 degrees C, 40 degrees C, and at almost constant water vapour pressure (8.5 to 11 torrs). For T1 = 22 degrees C and P1H20 = 8.5 torrs, the mean value of MEH20 is 29.5 +/- 1.6 mg of water per dm3 of ventilated gas (BTPS), while the values of WEV and WCV are respectively 8.1 +/- 1.9 watts and 1.6 +/- 0.4 watts. 2. When T1 increases, MEH20 and WEV increases and WCV decreases. Results show that WCV changes in sign and becomes a thermal gain when T1 is higher than core temperature. The total respiratory heat drain, convective plus evaporative, involved of the conditioning of respiratory gases is a small part of the total body heat balance (approximately 15%). However this heat drain which slowly decreases when T1 increases, represents the largest energy expenditure of the human organism in respiratory function.

Mechanics and energetics of stilt walking.

Three subjects were studied walking on a sports track with and without 1-m-long stilts. They were asked to walk in different ways. Pace length, step rate, heart rate, and oxygen consumption were measured under both conditions at different speeds. The results show that walking speed is generally faster for stilt walking than for normal walking. The higher speed is achieved due to increased pace length in spite of a decrease in step rate. The relationship between energy expenditure and walking speed is approximately the same in both cases. This result may be explained by two opposing factors: increase of pace length and decrease of step rate decrease the energy requirements of stilt walking, but the foot loading presented by the stilt walking exaggerates these conditions and increases energy expenditure.

Respiratory water loss.

Two kinds of studies have been conducted in order to measure respiratory water loss: a single breath study of instantaneous variations in relative gas humidity of air expired during one respiratory cycle and a multibreath study of the average values of water vapor in air expired during several successive cycles of steady state ventilation. In the first case, relative gas humidity is computed from results obtained by thermometry and mass spectrometry; in the second case, average water vapor content of expired air is calculated from plethysmographic spirometry and expired water collection. Both experiments showed that mixed expired gas is not fully water saturated. The multibreath study showed that the mass of water lost per liter of ventilated gas is not a function of ventilation per se but rather increases as tidal volume rises and decreases as respiratory frequency diminishes. The mass of water lost per cycle of steady state ventilation increases with tidal volume so that mean expired gas volume may be considered as a mixture of dry gas and water saturated gas. The single breath study showed that unsaturated gas is expired in the first part of expirate followed by wet saturated gas in the second part. The numerical values given by the two kinds of studies are in close agreement.