Expired Air Temperature Research Articles

Cold-induced changes in breathing pattern as a strategy to reduce respiratory heat loss

Thermoregulatory benefits of cold-induced changes in breathing pattern and mechanism(s) by which cold induces hypoventilation were investigated using male Holstein calves (1-3 mo old). Effects of ambient temperatures (Ta) between 4 and 18 degrees C on ventilatory parameters and respiratory heat loss (RHL) were determined in four calves. As Ta decreased, respiratory frequency decreased 29%, tidal volume increased 35%, total ventilation and RHL did not change, and the percentage of metabolic rate attributed to RHL decreased 26%. Total ventilation was stimulated by increasing inspired CO2 in six calves (Ta 4-6 degrees C), and a positive relationship existed between respiratory frequency and expired air temperature. Therefore, cold-exposed calves conserve respiratory heat by decreasing expired air temperature and dead space ventilation. Compared with thermoneutral exposure (16-18 degrees C), hypoventilation was induced by airway cold exposure (4-6 degrees C) alone and by exposing the body but not the airways to cold. Blocking nasal thermoreceptors with topical lidocaine during airway cold exposure prevented the ventilatory response but did not lower hypothalamic temperature. Hypothalamic cooling (Ta 16-18 degrees C) did not produce a ventilatory response. Thus, airway temperature but not hypothalamic temperature appears to control ventilation in cold-exposed calves.

Respiratory heat loss during work at various ambient temperatures

The purpose of this investigation was to establish the temperature and humidity of the expired air of subjects working at various metabolic rates at ambient temperatures between −40°C and 20°C in order to calculate respiratory heat loss. Measurements of the respired air temperature and water vapour content were made for five subjects while they either stood or walked on a treadmill. The results indicated that the maximum respired air temperature varied slightly with the ambient air temperature but changes in metabolic rate, respiration rate and breathing frequency had no apparent effect on the expired air temperature under the conditions studied. The relative humidity of the respired air was found to be close to saturation in the extreme-cold environments. Heat loss due to respiration was between 25 and 30% of the resting metabolic and between 15 and 20% of the working metabolic rate.

Thermoregulatory control of expired air temperature in diving harp seals.

Expired air temperature (Tex), metabolic rate (MR), and skin (Ts) and body (Tb; rectal) temperatures were recorded in four or five young (1-2 yr) harp seals (Phoca groenlandica) in air [mean air temperature (Ta) = -30, -10, or 10 degrees C] and in water [mean water temperature (Tw) = 2.3 or 24.8 degrees C, with Ta = -30, -10, 0, or 10 degrees C]. Apparent lower critical temperature was below -10 degrees C in air. Above this Ta, mean MR was 5.85 W.kg-0.75 (2.23 W.kg-1), while mean MR was 12.56 W.kg-0.75 (4.69 W.kg-1) at Ta -30 degrees C. When seals were immersed in water of 2.3 degrees C, mean MR was 6.13 W.kg-0.75 (2.31 W.kg-1), regardless of Ta. At Ta -30, -10, and 10 degrees C, mean Tex in air were 9.5, 13.0, and 25.0 degrees C, respectively. The corresponding values for seals in water (Tw = 2.3 degrees C) were 8.0, 9.5, and 15.5 degrees C, respectively. The low Tex recorded at Ta -30 and -10 degrees C in air and at all Ta in water (Tw = 2.3 degrees C) suggests that heat was conserved by nasal heat exchange. At Ta 10 degrees C, mean Tex of seals in air was approximately 10 degrees C higher than mean Tex of seals in water (Tw = 2.3 degrees C). Furthermore, seals subjected to a Tw of 24.8 degrees C at Ta 0 degrees C had a mean Tex 10 degrees C higher than when subjected to Tw 2.3 degrees C at the same Ta. These observations suggest that Tex in seals is under thermoregulatory control. In a series of forced dives of up to 5-min duration Tex was found to be the same before and after the dive regardless of dive duration and Ta.

Nasal heat and water exchange in gray seals.

Metabolic rate (MR), expired air temperature (Tex), respiratory frequency (f), respiratory minute volume (V), and skin (Ts) and body (Tb) temperatures were recorded in three gray seals (Halichoerus grypus) at ambient air temperatures (Ta) between -40 and +20 degrees C. At Ta within the thermoneutral zone, MR averaged 3.7 W.kg-0.75, while mean V was 0.26 1.min-1.kg-0.75. At Ta below -11 degrees C [apparent lower critical temperature (Tlc)], both MR and V increased linearly with decreasing Ta. Average maximum MR (9.6 W.kg-0.75) and V (0.57 1.min-1.kg-0.75) were both recorded at Ta of -40 degrees C. Tex decreased with decreasing Ta to an average minimum value of 8 degrees C at Ta of -30 degrees C. The highest Tex recorded was 32 degrees C at Ta of +20 degrees C. At Ta of -20 degrees C, both total respiratory heat loss, with one exception, and respiratory evaporative water loss reached their lowest values. At this Ta, 66% of the heat and 80% of the water added to the inspired air were regained on expiration. We suggest that nasal heat exchange may be of considerable importance for thermal and water balance in many pinnipeds.

Regulation of nasal heat exchange in reindeer

Previous studies have shown that reindeer are able to restrict respiratory heat loss by use of nasal heat exchange (Blix and Johnson, 1983). This mode of heat conservation, which is based on cooling of the expired air, and thereby condensation of water, particularly at low ambient temperatures, is possible because of the existence of a temperature gradient along the length of the nasal passages (Johnsen et ai, 1985a). Furthermore, Blix and Johnsen (1983) have shown that there is a summer to winter difference of about 12°C in exhaled air temperature at, for instance, —10°C ambient temperature, in these animals. At this ambient temperature respiratory minute volume and frequency were the same in summer and winter. This therefore indicates that the temperature gradient along the nasal mucosa in reindeer must be under physiological control. We have recently investigated the vascular anatomy of the reindeer head with particular emphasis on the nasal mucosa. Based on ideas which emanated from this work we have put forward a hypothesis for the operation and control of nasal heat exchange in reindeer (Johnsen et aL, 1985a). In order to visualize the vascular system of the reindeer head we have made use of uni-lateral plastic casts. These casts revealed that the nasal mucosa in reindeer consists of a network of frequently anastomosing arteries running the full length of the nasal turbinates in the anterior direction. This rete runs adjacent to and in close contact with a venous rete of similar complexity with which it communicates by way of capillaries and arterio-venous anastomoses. It was also evident from the plastic casts that the effluent from the venous rete can be drained through the deep sphenopalatine group of veins at the posterior end, and through the superficial dorsal nasal vein at the anterior end of the nasal cavity. The dorsal nasal vein in turn has a possibility to drain either directly into the jugular vein via the facial vein, or to the carotid rete for selective cooling of the brain. In situations of extreme heat conservation in the cold we suggest that the blood runs in opposite directions in the arterial and the venous rete of the nasal mucosa, whereby the temperature gradient along the nasal mucosa, which is necessary for cooling of the expired air, is maintained due to counter-current heat exchange. In this situation arterial inflow to the rete is low, and the dorsal nasal vein and the vessels of the anterior end of the venous rete are constricted. Accordingly, the venous effluent from the nasal mucosa is primarily drained through the sphenopalatine group of veins at a temperature close to that of the arterial blood. On the other hand, when the animal is in a state of extreme heat dissipation (in a hot environment, or during running), respiratory minute volume will increase substantially (Blix and Johnsen, 1983). However, an increase in respiratory minute volume without circulatory adjustments, will result in a substantial decrease of nasal mucosal temperature and a subsequent reduction in expired air temperature, which would compromise the dissipation of heat bv way of the respiratory tract. Under such heat

Exercise-induced angina in the cold

Exercise-induced angina (AP) is a common complaint of cardiac patients, particularly when exercising in the cold. To investigate the effects of environmental and inspired air temperature on AP, 9 patients with a history of cold-induced AP underwent progressive cycle ergometry tests in a climatic chamber on 4 separate occasions: (1) room environment (RE) (24 degrees C), and room inspired air (RA) (22.5 degrees C); (2) RE and cold inspired air (CA) (0.7 degrees C); (3) cold environment (CE) (-7.5 degrees C) and RA; and (4) CE and CA. Measurements of oxygen consumption, heart rate, blood pressure, and ventilation were made every minute and at test endpoint, which was either AP (85%) or fatigue (15% of all tests). Expired air temperature and skin temperature at 5 sites were also recorded. Results indicated that angina occurred sooner, and mean exercise time was significantly reduced in both RA/CE (-24%) and CA/CE (-15%) when compared with the RA/RE. Breathing CA in the RE did not significantly reduce exercise tolerance. Skin temperature was lower in both CE's compared to the RE's at all sites. Submaximal systolic blood pressure and calculated rate-pressure product were significantly higher in the CE's vs RE's. The adverse effects of cold on exercising angina patients are due to the earlier onset of angina, which appears to be induced more by the effects of exposure to the cold environment (-7.5 degrees C) than by cold air inhalation (0.7 degrees).

Central control of expired air temperature and other thermoregulatory effectors in reindeer.

Norwegian reindeer (Rangifer tarandus tarandus) were provided with chronically implanted hypothalamic perfusion thermodes to determine to what extent expired air temperature (Tex) is centrally controlled. The effects that alterations of hypothalamic temperature (Thy) had on metabolic heat production, respiratory frequency, respiratory evaporative heat loss, and rectal and leg-skin temperature were simultaneously recorded. Experiments were conducted in conscious animals exposed to ambient temperatures (Ta) of -20, 0, and 20 degrees C in summer, when fur insulation was minimal, and in winter, when it was prime. Altering Thy induced changes in Tex, the degree and direction of which depended on the prevailing Ta, season, and intensity of hypothalamic thermal stimulation. These results indicate that Tex, and hence nasal heat exchange, is under central control. The Thy-induced changes in the other measured parameters confirm that hypothalamic thermosensitivity in these animals is similar to that previously found in other mammalian species.

Ventilatory Oxygen Extraction During Cold Exposure in the Pigeon (Columba Livia)

ABSTRACT The respiratory responses to cold ambient temperatures in birds have only rarely been described. Bernstein & Schmidt-Nielsen (1974) studied the fish crow (Corvus ossifragus) during moderate cold exposure, while Bouverot, Hildwein & Oulhen (1976) measured ventilatory variables in pigeons (Columba livia) at near thermoneutral (22°C) and at cold (2°C) ambient temperatures. With respect to the amount of oxygen extracted from the ventilated air, both studies did not show any significant alterations correlated with changes in ambient temperature. However, several recent studies have demonstrated an increased oxygen extraction in response to cold exposure in birds [Bucher (1981) in the linneated parakeet (Bolborhynchos lineola), Brent, Rasmussen, Bech & Martini (1983) in the kittiwake (Rissa tridactyla), Brent, Pedersen, Bech & Johansen (1984) in the European coot (Fulica atra) and Bech, Johansen, Brent & Nicol (1984) in the duck (Anas platyrhynchos)). The significance of such an altered is obvious: the resultant decrease in ventilatory requirement will lower the relative loss of heat and water. Thus, together with a low expired air temperature (Schmidt-Nielsen, Hainsworth & Murrish, 1970), the increased oxygen extraction serves to minimize the respiratory heat and water loss in cold environments (Johansen & Bech, 1983).

The contribution of nasal countercurrent heat exchange to water balance in the northern elephant seal, Mirounga angustirostris.

Elephant seals fast completely from food and water for 1-3 months during terrestrial breeding. Temporal countercurrent heat exchange in the nasal passage reduces expired air temperature (Te) below body temperature (Tb). At a mean ambient temperature of 13.7 degrees C, Te is 20.9 degrees C. This results in the recovery of 71.5% of the water added to inspired air. The amount of cooling of the expired air (Tb - Te) and the percentage of water recovery varies inversely with ambient temperature. Total nasal surface area available for heat and water exchange, located in the highly convoluted nasal turbinates, is estimated to be 720 cm2 in weaned pups and 3140 cm2 in an adult male. Nasal temporal countercurrent heat exchange reduces total water loss sufficiently to allow maintenance of water balance using metabolic water production alone.

Is there a unifying hypothesis for exercise-induced asthma?

We believe that it is the loss of water per se and not heat loss that is the most important stimulus to exercise-induced asthma (EIA). The evidence to support this concept comes from a number of observations. First, EIA may occur when expired air temperature during exercise is close to body temperature and higher than that normally observed at rest. This suggests that EIA is not always associated with cooling of the airways. Second, there is evidence to show that the temperature of the inspired air is less critical than was previously thought. Providing that the water loss is the same, the airway response is reproducible even though the heat loss may vary because of differences in the temperature of the inspired air. Because expired water concentration is relatively constant, the airway response relates well to the water concentration of the inspired air. We believe that evaporative water loss from the airway mucosa induces a transient change in osmolarity in the epithelial fluid and that this change is a more potent stimulus to bronchoconstriction than is airway cooling. We believe this hypothesis accounts for many known facts about EIA and should merit further investigation by which it may be proved or disproved.

Temperature and Humidity of Expired Air: Interspecific Comparisons and Significance for Loss of Respiratory Heat and Water from Endotherms

The temperature of expired air at the external nares of black-tailed prairie dogs (Cynomys ludovicianus) was measured at inspired (ambient) air temperatures of 25, 30, 35, and 40 C, and over a broad range of humidities at each temperature. Expired air temperature was positively related to inspired air temperature and humidity; comparisons with published data for banner-tail kangaroo rats (Dipodomys spectabilis), deer mice (Peromyscus maniculatus), house mice (Mus musculus), and Australian hopping mice (Notomys alexis) showed similarities and differences among coefficients of multiple linear regressions describing analogous relationships. Simulations for a hypothetical mammal suggested how differences in the recovery of respiratory heat and water in nasal passages, and the loss of respiratory heat and water from the nose, should be affected by different relationships between the temperature of expired air and the temperature and humidity of inspired air.

Lung Ventilation and Temperature Regulation in the European Coot Fulica atra

Consumption of O₂ (V̇o2), production of CO₂ (V̇co2), respiratory frequency (f), tidal volume (VT), total inspired ventilation (V̇I), body temperature (Tb), and expired air temperature (Te) have been measured simultaneously in the coot, Fulica atra (mean body weight 0.398 kg), at ambient air temperatures (Ta) ranging from -25 C to 35 C. Below the lower critical temperature (20 C),V̇o2 increased according to the equation V̇o2 (ml O₂ kg⁻¹ min ⁻¹) = 37.52 − 0.97 Ta. At Ta of −25 Ca ventilation increase of 60% was markedly disproportional to the three- to fivefold increase in V̇o2. This implies a reduced air convection requirement (V̇I/V̇o2) of 48%. At Ta of 35 C, f doubled while VT remained nearly unchanged. A nearly unchanged V̇o2 associated with the increased V̇I at 35 C implies a functional bypass of the parabronchial segments of the lung. Expired air temperature shows a decline nearly parallel to an isothermal line between Te and Ta. At Ta of −10 C or lower, Te was within 2 C of zero. The respiratory responses to changes in Ta are discussed in terms of heat economy, showing that actual respiratory heat loss is only 9.6% of the theoretical maximum at −25 C. While 79.7% (at −25 C) can be ascribed to cooling of expired air, 10.7% is due to reduction in V̇I/V̇o2.

Barometric plethysmograph: advantages and limitations in recording infant respiration

The barometric plethysmograph enables recordings to be made of respiration in undisturbed unrestrained infants. Its use has been limited by practical difficulties and errors in calculation of tidal volume (VT). We describe a modification of the method that overcomes the practical difficulties and a series of studies in which the barometric method was directly compared with pneumotachograph measurements of VT in infants. The effects of respiratory pattern and expired air temperature plus the most appropriate formula for calculation of VT under different conditions are described.

Effect of spinal cord temperature on carotid blood flow in the Pekin duck.

Spinal cord heating in white Pekin ducks increases breathing rate and carotid blood flow. During naturally induced panting, the reverse effect was achieved by spinal cooling. An increased beak and expired air temperature during spinal heating suggest an importance of the increased carotid blood flow in maximizing heat dissipation during polypnoea. The results indicate that both the polypneic response and the increase in carotid blood flow are dependent on the same sensory input, namely the temperature of the spinal cord.

Allometry of respiratory and haematological parameters of arctic mammal

1. 1. The allometric relationships for minimum oxygen consumption and resting minute volume of summer acclimatized Arctic mammals were: V ̇ o 2 = 0.18 M 0.62, V ̇ min = 1.93 M 0.77, and the exponents of these relationships decreased with decreasing ambient temperature. 2. 2. Oxygen extraction of small mammals in thermoneutrality was 4–5% and decreased at low T a . Oxygen extraction of large mammals was lowest at high T a . 3. 3. Expired air temperatures decreased with decreasing air temperatures and differed substantially for different species. 4. 4. Calculated evaporative heat loss in thermoneutrality varied from about 5–16% in different species due to differences in oxygen extraction and expired air temperature. 5. 5. Blood of Arctic mammals has high red cell count, high haemoglobin concentration and low red cell volume compared to temperature zone mammals suggesting hemoconcentration as a mechanism of cold adaptation.

Metabolism, Respiration and Evaporative Water Loss in the Australian Hopping-Mouse Notomys Alexis (Rodentia: Muridae).

Resting oxygen consumption and total evaporative water loss were determined for N. alexis at ambient temperatures of 20, 28 and 33 deg C in dry air. The minimum rate of oxygen consumption was 0.61 ml min-1 at 33 deg C, and minimum total evaporative water loss was 4.75% body mass day-1 at 28 deg C. Respiration frequency, tidal volume and respiratory minute volume were determined for N. alexis at ambient temperatures of 20, 28 and 33 deg C in air of low or high relative humidity. Minimum values were obtained at 28 deg C and low RH for respiratory minute volume and tidal volume, and at 28 deg C and high RH for respiratory frequency. Expired air temperature of N. alexis at these temperatures was lower than or similar to ambient for mice in air of low RH, but was higher than or similar to ambient at high RH. Respiratory evaporative water loss, calculated from the previous data, was greatest for mice in dry air at 33 deg C, and least in moist air at 33 deg C. Cutaneous evaporative water loss made up about 40-60% of the total evaporative water loss for mice in dry air. The rates of total evaporative water loss were clearly reflected in the manner of body temperature regulation at high ambient temperatures. Hopping-mice in moist air at 28 and 33 deg C became hyperthermic, whereas mice in dry air showed only slight increases in body temperature. The significance of these data to hopping-mice in the field was discussed.

A Model of Respiratory Heat Transfer in a Small Mammal

A steady-state model of the heat and water transfer occurring in the upper respiratory tract of the kangaroo rat, Dipodomys spectabilis, is developed and tested. The model is described by a steady-state energy balance equation in which the rate of energy transfer from a liquid stream (representing the flow of heat and blood from the body core to the nasal region) is equated with the rate of energy transfer by thermal conduction from the nose tip to the environment. All of the variables in the equation except the flow rate of the liquid stream can be either measured directly or estimated from physiological measurements, permitting the solution of the equation for the liquid stream flow rate. After solving for the liquid stream flow rate by using data from three animals, the energy balance equation is used to compute values of energy transfer, expired air temperature, rates of water loss, and efficiency of vapor recovery for a variety of ambient conditions. These computed values are compared with values measured or estimated from physiological measurements on the same three animals, and the equation is thus shown to be internally consistent. To evaluate the model's predictive value, calculated expired air temperatures are compared with measured expired air temperatures of eight additional animals. Finally, the model is used to examine the general dependence of expired air temperature, of rates of water loss, and of efficiency of vapor recovery on ambient conditions.

The Maximum Temperature of Expired Air as a Rapid Measure of Human Body Temperature

The Maximum Temperature of Expired Air as a Rapid Measure of Human Body Temperature