Expired Air Temperature Research Articles

Fluxo de calor sensível e latente de codornas japonesas mantidas em diferentes ambientes térmicos

ABSTRACT This study aimed to estimate the heat flux through sensitive mechanisms and respiratory evaporation of Japanese quails kept in thermoneutral and warm environments, using simple environmental and physiological measures. 192 nine-week-old quails were used, distributed in a completely randomized design at two temperatures (T1 = 24°C and T2 = 32°C), with 12 replicates of eight birds each, with an experimental period of 63 days, divided into three 21-day periods. Physiological measurements of respiratory rate (RR), cloacal temperature (TC), and body surface temperature (TS) were measured twice a week. The behavior of the energy balance in the climatic chambers was obtained using the total thermal energy exchanges per unit surface area of the birds, derived from the sum of sensible (radiation and convection) and latent heat exchanges. Respiratory rate (P<.0001), surface temperature (P<.0001), and cloacal temperature (P=0.0047) were higher in the 32°C environment. The expired air temperature (P<.0001) and heat loss by respiratory evaporation (P<.0001) showed higher values when the quails were in an environment of 32°C, while the heat losses by convection (P<.0001) and radiation (P<.0001) were higher in a thermal comfort environment. In Japanese quails kept in a controlled environment, sensible heat dissipation by convection is the main way to eliminate excess thermal energy, when the air temperature is up to 32ºC.

Surviving heat: Resilience of Nellore bulls to solar radiation exposure

Surviving heat: Resilience of Nellore bulls to solar radiation exposure

Thermal modeling of the respiratory turbinates in arctic and subtropical seals

Mammals possess complex structures in their nasal cavities known as respiratory turbinate bones, which help the animal to conserve body heat and water during respiratory gas exchange. We considered the function of the maxilloturbinates of two species of seals, one arctic (Erignathus barbatus), one subtropical (Monachus monachus). By means of a thermo-hydrodynamic model that describes the heat and water exchange in the turbinate region we are able to reproduce the measured values of expired air temperatures in grey seals (Halichoerus grypus), a species for which experimental data are available. At the lowest environmental temperatures, however, this is only possible in the arctic seal, and only if we allow for the possibility of ice forming on the outermost turbinate region. At the same time the model predicts that for the arctic seals, the inhaled air is brought to deep body temperature and humidity conditions in passing the maxilloturbinates. The modeling shows that heat and water conservation go together in the sense that one effect implies the other, and that the conservation is most efficient and most flexible in the typical environment of both species. By controlling the blood flow through the turbinates the arctic seal is able to vary the heat and water conservation substantially at its average habitat temperatures, but not at temperatures around −40 °C. The subtropical species has simpler maxilloturbinates, and our model predicts that it is unable to bring inhaled air to deep body conditions, even in its natural environment, without some congestion of the vascular mucosa covering the maxilloturbinates. Physiological control of both blood flow rate and mucosal congestion is expected to have profound effects on the heat exchange function of the maxilloturbinates in seals.

Does control of insensible evaporative water loss by two species of mesic parrot have a thermoregulatory role?

Insensible evaporative water loss (EWL) at or below thermoneutrality is generally assumed to be a passive physical process. However, some arid zone mammals and a single arid zone bird can control their insensible water loss, so we tested the hypothesis that the same is the case for two parrot species from a mesic habitat. We investigated red-rumped parrots (Psephotus haematonotus) and eastern rosellas (Platycercus eximius), measuring their EWL, and other physiological variables, at a range of relative humidities at ambient temperatures of 20 and 30°C (below and at thermoneutrality). We found that, despite a decrease in EWL with increasing relative humidity, rates of EWL were not fully accounted for by the water vapour deficit between the animal and its environment, indicating that the insensible EWL of both parrots was controlled. It is unlikely that this deviation from physical expectations was regulation with a primary role for water conservation because our mesic-habitat parrots had equivalent regulatory ability as the arid habitat budgerigar (Melopsittacus undulatus). This, together with our observations of body temperature and metabolic rate, instead support the hypothesis that acute physiological control of insensible water loss serves a thermoregulatory purpose for endotherms. Modification of both cutaneous and respiratory avenues of evaporation may be involved, possibly via modification of expired air temperature and humidity, and surface resistance.

Differences between times of day for the basic physiological traits of Nellore bulls exposed to solar radiation

ABSTRACT The aim of this study was to evaluate the basic physiological traits of Nellore bulls exposed to solar radiation at different times of the day. Sixteen Nellore bulls with an average age of 3 years were used. Air temperature (Ta, °C), relative humidity (RH, %), wind speed (U, m/s) and solar radiation (Rs, W/m2) were the meteorological variables evaluated during the study. Respiratory rate (Fr, breaths/min), rectal temperature (Tr, °C), body surface temperature (Ts, °C) and expired air temperature (Texp, °C) were evaluated as physiological traits. The highest Fr and Ts averages were observed from 11:00 to 14:00 (36.34 breaths/min and 37.62 °C, respectively). Texp presented increasing values throughout the day, with its highest average (33.35 °C) between 15:00 and 17:00. The Tr did not present significant variation between the times of day. It is concluded that intense Rs and high Ta during the hottest times of day induce Nellore bulls to trigger thermoregulatory mechanisms, such as the respiratory system, to maintain body temperature within narrow limits.

Athletes Do Not Condition Inspired Air More Effectively than Nonathletes during Hyperpnea.

Twenty-three endurance athletes from various sports, 12 with airway hyperresponsiveness (AHR) and/or exercise-induced bronchoconstriction (EIB) (A+), 11 without AHR and/or EIB (A-), 12 nonathletes with AHR and/or EIB (C+), and 11 nonathletes without AHR and/or EIB (C-) were recruited. All subjects attended the laboratory on three occasions, twice for baseline characterization, including questionnaires, pulmonary function, methacholine bronchoprovocation, allergy skin prick tests, exhaled nitric oxide measurement, and a standard EVH, and once to perform a modified EVH to assess ΔT. Inspired and expired air temperatures were measured with a high-precision probe during EVH and at regular intervals until 30 min after the end of the test. The global ΔT during the EVH was +5.8°C ± 1.5°C and +4.7°C ± 1.5°C during the 30 min after the EVH. No difference was found between groups for either the ΔT or the slope of ΔT, during and after the EVH. This study shows no evidence of improved capacity to condition inspired air in endurance athletes, which could have suggested an increased bronchial blood flow or another adaptive mechanism. The absence of an adaptive mechanism could therefore contribute to airway damage observed in athletes in allowing colder but mainly dryer air to penetrate deeper in the lung.

Models to predict both sensible and latent heat transfer in the respiratory tract of Morada Nova sheep under semiarid tropical environment.

The aim of this study was to build a prediction model both sensible and latent heat transfer by respiratory tract for Morada Nova sheep under field conditions in a semiarid tropical environment, using easily measured physiological and environmental parameters. Twelve dry Morada Nova ewes with an average of 3±1.2years old and average body weight of 32.76±3.72kg were used in a Latin square design 12×12 (12days of records and 12 schedules). Tidal volume, respiratory rate, expired air temperature, and partial vapor pressure of the expired air were obtained from the respiratory facial mask and using a physiological measurement system. Ewes were evaluated from 0700 to 1900h in each day under shade. A simple nonlinear model to estimate tidal volume as a function of respiratory rate was developed. Equation to estimate the expired air temperature was built, and the ambient air temperature was the best predictor together with relative humidity and ambient vapor pressure. In naturalized Morada Nova sheep, respiratory convection seems to be a mechanism of heat transfer of minor importance even under mild air temperature. Evaporation from the respiratory system increased together with ambient air temperature. At ambient air temperature, up to 35°C respiratory evaporation accounted 90% of the total heat lost by respiratory system, on average. Models presented here allow to estimate the heat flow from the respiratory tract for Morada Nova sheep bred in tropical region, using easily measured physiological and environmental traits as respiratory rate, ambient air temperature, and relative humidity.

Thermal equilibrium responses in Guzerat cattle raised under tropical conditions

The literature is very sparse regarding research on the thermal equilibrium in Guzerat cattle (Bos indicus) under field conditions. Some factors can modify the physiological response of Guzerat cattle, such as the reactivity of these animals to handling. Thus, the development of a methodology to condition and select Guzerat cattle to acclimate them to the routine collection of data without altering their physiological response was the objective of the preliminary experiment. Furthermore, the animals selected were used in the main experiment to determine their thermal equilibrium according to the thermal environment. For this proposal, the metabolic heat production and heat exchange between the animal and the environment were measured simultaneously in the field with an indirect calorimetry system coupled to a facial mask. The results of the preliminary experiment showed that the respiratory rate could demonstrate that conditioning efficiently reduced the reactivity of the animals to experimental handling. Furthermore, the respiratory rate can be used to select animals with less reactivity. The results of the main experiment demonstrate that the skin, hair-coat surface and expired air temperature depend on the air temperature, whereas the rectal temperature depends on the time of day; consequently, the sensible heat flow was substantially reduced from 70 to 20Wm−2 when the air temperature increased from 24 to 34°C. However, the respiratory latent heat flow increased from 10 to 15Wm−2 with the same temperature increase. Furthermore, the metabolic heat production remained stable, independent of the variation of the air temperature; however, it was higher in males than in females (by approximately 25%). This fact can be explained by the variation of the ventilation rate, which had a mean value of 1.6 and 2.2Ls−1 for females and males, respectively.

Thermal equilibrium of goats

The effects of air temperature and relative humidity on thermal equilibrium of goats in a tropical region was evaluated. Nine non-pregnant Anglo Nubian nanny goats were used in the study. An indirect calorimeter was designed and developed to measure oxygen consumption, carbon dioxide production, methane production and water vapour pressure of the air exhaled from goats. Physiological parameters: rectal temperature, skin temperature, hair-coat temperature, expired air temperature and respiratory rate and volume as well as environmental parameters: air temperature, relative humidity and mean radiant temperature were measured. The results show that respiratory and volume rates and latent heat loss did not change significantly for air temperature between 22 and 26°C. In this temperature range, metabolic heat was lost mainly by convection and long-wave radiation. For temperature greater than 30°C, the goats maintained thermal equilibrium mainly by evaporative heat loss. At the higher air temperature, the respiratory and ventilation rates as well as body temperatures were significantly elevated. It can be concluded that for Anglo Nubian goats, the upper limit of air temperature for comfort is around 26°C when the goats are protected from direct solar radiation.

Comparative physiology of Australian quolls (Dasyurus; Marsupialia)

Quolls (Dasyurus) are medium-sized carnivorous dasyurid marsupials. Tiger (3,840 g) and eastern quolls (780 g) are mesic zone species, northern quolls (516 g) are tropical zone, and chuditch (1,385 g) were once widespread through the Australian arid zone. We found that standard physiological variables of these quolls are consistent with allometric expectations for marsupials. Nevertheless, inter-specific patterns amongst the quolls are consistent with their different environments. The lower T (b) of northern quolls (34 degrees C) may provide scope for adaptive hyperthermia in the tropics, and they use torpor for energy/water conservation, whereas the larger mesic species (eastern and tiger quolls) do not appear to. Thermolability varied from little in eastern (0.035 degrees C degrees C(-1)) and tiger quolls (0.051 degrees C degrees C(-1)) to substantial in northern quolls (0.100 degrees C degrees C(-1)) and chuditch (0.146 degrees C degrees C(-1)), reflecting body mass and environment. Basal metabolic rate was higher for eastern quolls (0.662 +/- 0.033 ml O(2) g(-1) h(-1)), presumably reflecting their naturally cool environment. Respiratory ventilation closely matched metabolic demand, except at high ambient temperatures where quolls hyperventilated to facilitate evaporative heat loss; tiger and eastern quolls also salivated. A higher evaporative water loss for eastern quolls (1.43 +/- 0.212 mg H(2)O g(-1) h(-1)) presumably reflects their more mesic distribution. The point of relative water economy was low for tiger (-1.3 degrees C), eastern (-12.5 degrees C) and northern (+3.3) quolls, and highest for the chuditch (+22.6 degrees C). We suggest that these differences in water economy reflect lower expired air temperatures and hence lower respiratory evaporative water loss for the arid-zone chuditch relative to tropical and mesic quolls.

Noncontact Vital Sign Monitoring System for Isolation Unit (Casualty Care System)

For measuring the vital signs of casualties inside an isolation unit, we developed a noncontact vital sign monitoring system using a microwave radar. The system was tested on eight healthy volunteers ranging in age from 30 to 48 years. The heart and respiratory rates derived by the microwave radar correlated with the heart and respiratory rates determined by electrocardiogram and respiratory sensor (r = 0.98, p < 0.0001 for heart rate; r = 0.84, p < 0.01 for respiratory rate). The exhaled CO and CO2, as a measure of trauma injury, were measured using an exhaled gas analyzer. The CO and CO2 concentrations were found to average 3.8 +/- 4.3 ppm and 2.9 +/- 0.4%, respectively. The expired air temperature and body temperature, as indicators of hemorrhagic hypothermia, averaged 31.8 +/- 1.7 degrees C and 36.2 +/- 0.4 degrees C, respectively. The results show that our system is promising for future prehospital application in determining casualty conditions for fluid infusions by the Casualty Care System intravenous lines.

Respiratory heat loss of Holstein cows in a tropical environment

In order to develop statistical models to predict respiratory heat loss in dairy cattle using simple physiological and environmental measurements, 15 Holstein cows were observed under field conditions in a tropical environment, in which the air temperature reached up to 40 degrees C. The measurements of latent and sensible heat loss from the respiratory tract of the animals were made by using a respiratory mask. The results showed that under air temperatures between 10 and 35 degrees C sensible heat loss by convection decreased from 8.24 to 1.09 W m(-2), while the latent heat loss by evaporation increased from 1.03 to 56.51 W m(-2). The evaporation increased together with the air temperature in almost a linear fashion until 20 degrees C, but it became increasingly high as the air temperature rose above 25 degrees C. Convection was a mechanism of minor importance for respiratory heat transfer. In contrast, respiratory evaporation was an effective means of thermoregulation for Holsteins in a hot environment. Mathematical models were developed to predict both the sensible and latent heat loss from the respiratory tract in Holstein cows under field conditions, based on measurements of the ambient temperature, and other models were developed to predict respiration rate, tidal volume, mass flow rate and expired air temperature as functions of the ambient temperature and other variables.

Thermoregulatory physiology of the Crested Pigeon Ocyphaps lophotes and the Brush Bronzewing Phaps elegans.

The metabolic physiology of the Crested Pigeon (Ocyphaps lophotes) and the Brush Bronzewing (Phaps elegans) is generally similar to that expected for birds of their size, but the Crested Pigeon has a number of characteristics which would aid survival in hot and dry regions. Body temperature increased similarly for the Crested Pigeon (from 38.8 degrees C to 41.5 degrees C) and the Brush Bronzewing (39.3 degrees C to 41.4 degrees C) over ambient temperatures (T(a)s) from 10 degrees C to 35 degrees C. Both species became hyperthermic (body temperature, T(b)>42 degrees C) at T(a)=45 degrees C. Basal metabolic rate of the Crested Pigeon (0.65 ml O(2) g(-1) h(-1) at 40 degrees C) was approximately 71% of that predicted for a columbid bird, while BMR of the Brush Bronzewing (0.87 ml O(2) g(-1) h(-1) at 20 degrees C to 40 degrees C) was approximately 102% of predicted. Total evaporative water loss increased exponentially with T(a) for both species, from <1 mg H(2)O g(-1) h(-1) at 10 degrees C to >12 mg H(2)O g(-1) h(-1) at 45 degrees C. It was similar and low for both species at T(a)<30 degrees C, but was higher for the Brush Bronzewing than the Crested Pigeon at T(a)>30 degrees C. Ventilatory minute volume matched oxygen consumption, such that oxygen extraction efficiency did not change with T(a) and was similar for both species (approximately 20%). Expired air temperature was considerably lower than T(b) for both species at T(a)<35 degrees C, potentially reducing respiratory water loss by approximately 65% at T(a)=10 degrees C to approximately 30% at T(a)=35 degrees C. Cutaneous evaporative cooling was significant for both species, with skin resistance decreasing as T(a) increased. The Crested Pigeon had a lower skin resistance than the Brush Bronzewing at T(a)=45 degrees C. The Brush Bronzewing had apparently reached its maximum cutaneous water loss at 30 degrees C and relied on panting to cool at higher T(a).

Effects of ventilation and pleural effusion on measurements of airway thermal volume and blood flow in dog lungs.

We studied the effects of ventilation and pleural effusion on measurements of airway thermal volume (ATV) and pulmonary blood flow (PBF) by using the airway gas thermometry method of V. B. Serikov, M. S. Rumm, K. Kambara, M. I. Bootomo, A. R. Osmack, and N. C. Staub (J. Appl. Physiol. 72: 944-953, 1992) in 39 anesthetized dogs with or without lung edema or pleural effusion. To examine the differential effects of increased-pressure and increased-permeability lung edema on accuracy and sensitivity of ATV and PBF, two models of lung edema were induced by intravenous infusion of a Dextran 70 solution and alloxan monohydrate, respectively. Dogs were hyperventilated for 3 min by using a wide range of minute ventilation (VE) to produce two steady-state conditions of airway temperature. Higher levels of VE increased an estimated amount of ATV. The ATV produced by hyperventilation at VE values of 559, 158, and 72 ml.min-1.kg-1 was consistent with the gravimetric total lung mass, the blood-free wet lung weight, and the extravascular lung water volume, respectively. The coefficient of lung thermal conductivity, a practical index of the rate of heat conduction through tissue from lung vessels, was related to the ratio of the decrease in expired air temperature to VE, and estimated PBF was consistent with the thermodilution cardiac output. Pleural effusion had little effect on measurements of ATV and PBF. However, ATV and PBF showed increased variation in dogs with dextran-induced lung edema.

Expired air temperature during steady-state running

While some metabolic measurement systems measure expiratory temperature to standardize gas volumes, other systems use only an estimate. This study investigated the effect of prolonged exercise on expiratory temperature near the pneumotachometer to provide a basis for its estimation when actual measurement is unavailable. Seven active females each performed two 45-min treadmill runs at identical speeds (64.5% +/- 11.8% of VO2max) in which the pneumotachometer heater control was either set to 37 degrees C or turned off. Expired air temperatures were monitored with thermocouples at the nonrebreathing valve (VAL) and 1 cm upstream (UPS) and downstream (DNS) from the pneumotachometer screens. There were no temperature differences over time for any of the conditions, and there were no differences in the VAL or UPS temperatures between the heated and unheated conditions. DNS temperature was higher during the heated condition at all time periods (P < 0.01). Mean DNS temperatures for the heated and unheated condition were 30.2 +/- 1.0 degree C and 27.9 +/- 1.1 degrees C, respectively. We conclude that expired air temperatures near the pneumotachometer remain stable during extended steady-state exercise regardless of whether the pneumotachometer is heated or not.

Nasal heat and water exchange is not an effector mechanism for water balance regulation in grey seals.

Phocid seals may effectively restrict respiratory heat and water loss by nasal heat and water exchange (NHE), and respiratory heat loss is, in fact, subject to thermoregulatory control. We have investigated whether phocid seals also control NHE and respiratory water loss to regulate water balance. Three resting juvenile female grey seals (Halichoerus grypus) were subjected to: (i) 5 days of food and water deprivation, (ii) intravenous infusion of 1000 ml of a hypersomotic (930 mM) solution of the diuretic mannitol, and (iii) oral injection of 1500 ml distilled water. During these experiments in air of 0 degree C, expired air temperature (T(ex)) and respiratory frequency (f) were recorded, and urine and blood samples collected. The results were compared with results from control experiments. Five days of food and water deprivation caused an average 10.5% and 20.8% increase in plasma (PO) and urine (UO) osmolality, respectively. Mannitol infusion induced excessive diuresis and caused an average 2.45% reduction of the estimated body water pool. Water loading caused an average 4.5% and 60% reduction in PO and UO, respectively, while urine production increased by 365%, on average. However, in no case did either T(ex) or f change significantly from mean control levels of 22.4 (range: 20.7-25.2) degrees C and 7.3 (range: 6.6-8.4) breaths min-1, respectively. Thus, water balance disturbances that initiate renal compensatory mechanisms fail to affect NHE in grey seals. This suggests that control of NHE is not an effector mechanism for regulation of water balance in grey seals.

Expired air temperature at the mouth during a maximal forced expiratory manoeuvre

We have studied the temperature of expired air during a maximal forced expiratory manoeuvre, because this has not previously been fully investigated and it will influence how flow and volume recording devices should be calibrated and used. Temperature was recorded with a fine thermocouple, the response time of which was determined at various gas velocities and for which a correction was made. Recordings during maximal forced expiratory manoeuvres were made on 12 normal subjects and 12 subjects with chronic airflow limitation. The thermocouple was placed in the mouthpiece, so that it was at the level of the lips during a blow. In the normal subjects, the effect of differing inhalation protocols was also determined. In the normal subjects, the mean temperature was 33.6 degrees C at peak expiratory flow (PEF), and 34.4 degrees C at 75% forced vital capacity (FVC), but fell to 33.4 degrees C at FVC. In the subjects with chronic airflow limitation, the temperature was constant at 35.0 degrees C from PEF up to 50% FVC, being significantly higher than in the normals, and fell to 33.5 degrees C at FVC. Expired air temperature up to 50% FVC was significantly negatively correlated with absolute PEF, forced expiratory volume in one second (FEV1) and FVC. In the normals, a slow inhalation through the nose raised the expired temperature by almost 1 degree C throughout the blow, whereas inhaling air at 6 degrees C did not affect expired air temperature. The expired air temperature can vary by up to 3 degrees C between individual subjects, and it is influenced by the route of inhalation and the inspired volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Water and Energy Limitations on Flight Duration in Small Migrating Birds

-We examined the physiological limitations to flight duration in small migrating birds with a computer-simulation model. Given preflight body mass, fat and water contents, and flight-path meteorological data, we calculated water and energy budgets and possible flight time. The model can be applied to birds of any size that migrate by flapping flight. As an example, we simulated the flight of small Palearctic passerines (body mass = 10 g) during their annual migration over the Sahara desert. Sensitivity analysis of model input variables indicated that oxygen extraction and expired air temperature are the most important physiological variables in a bird's water budget and can profoundly influence flight duration. This manifests the importance of: (1) efficient cooling in the nasal passages of flying birds; and (2) the choice of flight altitude (which affects both ambient air temperature and expired air temperature). The model predicted that: (1) Prior to migration, these birds must have stored fat comprising at least 22% of their initial body mass; otherwise, they cannot complete their journey. (2) In relatively fat birds (stored fat > 0.22 body mass), dehydration rather than energy will limit flight duration. (3) Birds should fly at an altitude not exceeding 1,000 m to cross the Sahara successfully. (4) Even in low-flying fat birds, flight duration will be limited by their stringent water budget. The model further predicted that small passerines cannot cross the Sahara in a 30to 40-h nonstop flight, as commonly accepted, but should confine flying to the cooler hours (i.e. nights) and rest during the day in order to avoid elevated rates of water loss due to higher ambient air temperatures. Available data and observations of birds trapped at stopover sites in the Sahara support these predictions. Received 26 February 1991, accepted 13 January 1992. LONG-DISTANCE flight over seas or deserts is perhaps the most risky and physiologically challenging event in the life cycle of migratory birds (Moreau 1961, Wilson 1981). Reports of high attrition among migrants and of exhausted birds found severely dehydrated and/or fat depleted (Serle 1956, Odum et al. 1964, Rogers and Odum 1964, Johnston 1968, Wilson 1981) raised the question: Is water or energy the greater physiological limitation to bird flight duration? Energy, rather than water, is currently considered the major factor limiting bird flight duration because dehydration can be avoided by flying at high altitudes where air temperatures are low (Blem 1976, Torre-Bueno 1978, Skadhauge 1981, Dawson 1982, Biesel and Nachtigall 1987, Biebach 1990). However, this paradigm has not been substatiated with empirical field

Application of respiratory heat exchange for the measurement of lung water.

A noninvasive method for measuring pulmonary blood flow and lung mass (called airway thermal volume), based on the measurements of lung heat exchange with environment, is described. The lungs function as a steady-state heat exchange system, having an inner heat source (pulmonary blood flow) and an external heat sink (ventilation). Sudden changes in the steady-state condition, such as caused by hyperventilation of dry air, lead to a new steady state after a few minutes. The expired air temperature difference between the initial and final steady states is proportional to pulmonary blood flow, whereas the rate at which the new steady state is achieved is proportional to airway thermal volume. The method was tested in 20 isolated dogs lungs, 9 perfused goat lungs, and 27 anesthetized sheep. The expired air temperature fall during hyperventilation was inversely proportional to the perfusion rate of the isolated lungs, and half-time of the temperature fall was proportional to the lung tissue mass. Experiments in anesthetized sheep showed that the measured airway thermal volume is close to the total mass of the excised lungs, including its residual blood (r = 0.98). Pulmonary edema and fluid instillation into the bronchial tree increased in the measured lung mass.

THE PHYSIOLOGICAL COST OF WEARING A DISPOSABLE RESPIRATOR

In order to gain an understanding of the physiological stresses imposed by the wearing of a single-use disposable respirator, a series of experiments was done to measure the cardiopulmonary effects of wearing the respirator (heart rate, respiratory rate, and blood pressure); resistance to breathing while wearing a respirator; and heat stress imposed by the use of a respirator (changes in inspired and expired air temperature). Ten men, ages 24 to 35, of varying fitness levels, served as volunteers in the studies. All the men exercised on a treadmill both with and without 3M Model 8715 disposable respirators. Workloads corresponding to light, moderate, and heavy levels were calculated for each volunteer based on his maximal oxygen uptake. As work intensity increased, an increase in breathing resistance was found. Peak resistances were in the range of +/- 2 cm water. Work-intensity level increases in respiratory rates were found with and without the respirators, but the respirator use trial had a significantly increased respiratory rate. Heart rate also showed a dose-related increase as work intensity increased and was significantly greater in the respirator trials at heavy levels of work and during recovery. Systolic blood pressure showed a biphasic response to respirator use, being significantly lower at rest and higher at high levels of work. Diastolic blood pressure changes were less dramatic but were elevated in the respirator trials. Clinically important increases in blood pressure were found in two volunteers when respirators were worn. Air temperatures immediately anterior to the face were, on average, 7.5 degrees C higher in the respirator trials.(ABSTRACT TRUNCATED AT 250 WORDS)