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S R Muza

Publications and source records attributed to S R Muza.

At least 37 records · Page 2Linked to original sources
PubMed1997

Exercise responses after altitude acclimatization are retained during reintroduction to altitude.

Following 2 to 3 wk of altitude acclimatization, ventilation is increased and heart rate (HR), plasma volume (PV), and lactate accumulation ([La]) are decreased during submaximal exercise. The objective of this study was to determine whether some degree of these exercise responses associated with acclimatization would be retained upon reintroduction to altitude (RA) after 8 d at sea level (SL). Six male lowlanders (X +/- SE; 31 +/- 2 yr, 82.4 +/- 4.6 kg) exercised to exhaustion at the same relative percentages of peak oxygen uptake (VO2peak) at SL, on acute altitude (AA) exposure, after a 16-d chronic altitude (CA) exposure on Pikes Peak (4,300 m), and during a 3- to 4-h RA in a hypobaric chamber (4,300 m; 446 mm Hg) after 8 d at SL. The submaximal exercise to exhaustion time (min) was the same at SL (66.0 +/- 1.6), AA (67.7 +/- 7.3), CA (79.9 +/- 6.2), and RA (67.9 +/- 1.9). At 75% VO2peak: (1) arterial oxygen saturation (SaO2) increased from AA to CA (67.0 +/- 1.5 vs 78.5 +/- 1.8%; P < 0.05) and remained increased at RA (77.0 +/- 2.0%); (2) HR decreased from SL to CA (171 +/- 6 vs 152 +/- 9 beats x min-1; P < 0.05) and remained decreased at RA (157 +/- 5 beats x min-1); (3) calculated PV decreased 6.9 +/- 10.0% at AA, 21.3 +/- 11.1% at CA, and 16.7 +/- 5.4% at RA from SL baseline values, and (4) [La] decreased from AA to CA (5.1 +/- 0.9 vs 1.9 +/- 0.4 mmol x L-1; P < 0.05) and remained decreased at RA (2.6 +/- 0.6 mmol x L-1). Upon RA after 8 d at SL, the acclimatization responses were retained 92 +/- 9% for SaO2, 74 +/- 8% for PV, and 58 +/- 3% for [La] at 75% VO2peak. In conclusion, although submaximal exercise to exhaustion time is not improved upon reintroduction to altitude after 8 d at sea level, retention of beneficial exercise responses associated with altitude acclimatization is likely in individuals whose work, athletic competition, or recreation schedules involve intermittent sojourns to high elevations.

Acclimatization↗
PubMed1997

Ventilatory capacities at sea level and high altitude.

Because air is less dense at high altitude (HA), airway resistance is reduced and maximum inspiratory and expiratory flows are greater than at sea level (SL). Despite the reduction in airway resistance, ventilatory muscle endurance may be decreased by hypobaric hypoxia and, thus, may be a factor in limiting exercise at HA. To explore the effects of HA on ventilatory capacities and their relation to ventilatory demands of exercise, we measured 15-s maximum voluntary ventilation (MVV), 15-min maximum sustainable ventilation (MSV), and maximum airway pressures (Plmax and PEmax) in 18 healthy young men at SL and HA (Pikes Peak, 4300 m, or hypobaric chamber, PB approximately 460 mmHg). In eight of these subjects ventilatory capacities were compared with exercise ventilations. We also measured the effects of 36% O2 on the MSV in 12 of the subjects exposed to simulated altitude. Similar results were obtained at either simulated or actual HA. We found that MVV increased (p < 0.001) by 20% and the MSV (p < 0.001) by 15% at HA. Administration of 36% O2 at HA increased MSV further by 5% with no effect on MVV. No effect of HA on maximum inspiratory and expiratory pressures was found. We confirmed previous findings of modest increases in forced 1-s expired volume (FEV1) and slight decreases in forced vital capacity (FVC) at HA. At both SL and HA, the MSV exceeded the ventilatory demands of submaximal cycle exercise that could be sustained for about 30 min. During progressive cycle exercise to exhaustion, however, peak VE was not different from MVV, either at SL or HA. We conclude that the small, but significant, increase in MSV with 36% O2 administration at HA suggests that hypoxia decreases ventilatory endurance for flow loads as determined by the MSV. Thus, the possibility that ventilatory limits have a role in cessation of exercise at high altitude cannot be ruled out.

Adult↗
PubMed1996

Inspiratory resistance effects on exercise breathing pattern relationships to chemoresponsiveness.

This study examined the effects of added inspiratory resistance (R5 5 cm H2O.L-1.S-1) on the relationship between exercise breathing pattern and resting hypercapnic ventilatory responsiveness (HCVR). Twelve men completed an HCVR test and two progressive intensity exercise tasks with minimal (R0) and elevated (R5) resistance. Peak oxygen uptake, and peak power output were not different, but peak VE was decreased with the R5 load. Exercise ventilation (VE was tightly coupled to VCO2 (r = 0.97) as was mean inspiratory flow rate (VT/TI, r = 0.95), but not duty cycle (TI/TTOT, r = 0.39). With imposition of R5, VT/TI was depressed (p < 0.05) at mild (approximately 40% VO2peak) to peak exercise intensities, whereas TI/TTOT was relatively unaffected. At both moderate (approximately 60% peak VO2) and peak exercise intensities, VE was positively correlated (r = 0.62, p < 0.05 and r = 0.82, p < 0.01, respectively) to subjects' HCVR. However, when normalized, VE.VCO2(-1) was significantly correlated to HCVR only at peak exercise ventilation during the R0 load. Analysis of the exercise breathing pattern revealed that at both moderate and peak exercise intensities, VT/TI was positively correlated to HCVR, but TI/TTOT was not. The imposition of R5 decreased the slope of the relationship between exercise VT/TI and HCVR at both moderate and peak exercise intensities, and weakened the positive correlation at the moderate exercise intensity. Our analysis indicates that: 1) the positive correlation between exercise hyperpnea and HCVR is mediated by the mean inspiratory flow rate rather than the duty cycle component of the breathing pattern and, 2) at moderate exercise the relationship between mean inspiratory flow rate and resting HCVR is more sensitive to added inspiratory resistance than minute ventilation per se. These findings suggest that the degree of influence resting HCVR has on exercise hyperpnea is dependent upon the magnitudes of both the ventilatory hyperpnea and mechanical loading placed on the ventilatory system.

Adult↗
PubMed1996

Effect of lung volume on the respiratory action of the canine sternomastoid.

We tested the hypothesis that because the resting length of the canine sternomastoid (SM) muscles is relatively insensitive to lung volume change, the SM may maintain its inspiratory force generation regardless of lung volume. The relationships between SM pre- and postcontraction in situ fiber lengths and SM-produced inspiratory pressure generation [i.e., esophageal (Pes)] and rib cage displacements were examined in adult supine anesthetized dogs at residual volume (RV), functional residual capacity, and total lung capacity. SM muscle contraction was produced by isolated bilateral supramaximal electrical stimulation during hyperventilation-induced apnea. In all animals, SM contraction produced negative change in Pes (i.e., an inspiratory action). Passively increasing lung volume from RV to total lung capacity decreased (P < or = 0.01) the SM-produced Pes by -66 +/- 4% but had a relatively small effect on SM in situ pre- and postcontraction fiber length (< 3%). Whereas SM contraction at RV produced a cranial displacement of the sternum and increased the upper rib cage cross-sectional area, passively elevating lung volume diminished the SM-produced expansion of the upper rib cage. Hyperinflation did not increase the impedance of the sternum to cranial displacement during SM contraction, suggesting that hyperinflation caused a dissociation between the mechanical action of the sternum and the upper rib cage. These results suggest that mechanical dissociation of the ribs and sternum may diminish the contribution of the SM to inspiratory volume generation when breathing is done from elevated end-expiratory lung volumes.

Animals↗
PubMed1996

Effects of erythrocyte infusion on VO2max at high altitude.

This study investigated whether autologous erythrocyte infusion would ameliorate the decrement in maximal O2 uptake (VO2max) experienced by lowlanders when they ascend to high altitude. VO2max was measured in 16 men (treadmill running) at sea level (SL) and on the 1st (HA1) and 9th (HA9) days of high-altitude (4,300 m) residence. After VO2max was measured at SL, subjects were divided into two matched groups (n = 8). Twenty-four hours before ascent to high altitude, the experimental group received a 700-ml infusion of autologous erythrocytes and saline (42% hematocrit), whereas the control group received only saline. The VO2max of erythrocyte-infused [54 +/- 1 (SE) ml.kg-1.min-1] and control subjects (52 +/- 2 ml.kg-1.min-1) did not differ at SL before infusion. The decrement in VO2max on HA1 did not differ between groups, averaging 26% overall, despite higher (P < 0.01) arterial hematocrit, hemoglobin concentration, and arterial O2 content in the erythrocyte-infused subjects. By HA9, there were no longer any differences in hematocrit, hemoglobin concentration, or arterial O2 content between groups. No change in VO2max occurred between HA1 and HA9 for either group. Thus, despite increasing arterial O2-carrying capacity, autologous erythrocyte infusion did not ameliorate the decrement in VO2max at 4,300-m altitude.

Acclimatization↗
PubMed1996

Altitude acclimatization and blood volume: effects of exogenous erythrocyte volume expansion.

We studied sea-level residents during 13 days of altitude acclimatization to determine 1) altitude acclimatization effects on erythrocyte volume and plasma volume, 2) if exogenous erythrocyte volume expansion alters subsequent erythrocyte volume and plasma volume adaptations, 3) if an increased blood oxygen content alters erythropoietin responses during altitude acclimatization, and 4) mechanisms responsible for plasma loss at altitude. Sixteen healthy men had a series of hematologic measurements made at sea level, on the first and ninth days of altitude (4,300 m) residence, and after returning to sea level. Twenty-four hours before the ascent to altitude, one group received a 700-ml infusion of autologous erythrocytes (42% hematocrit), whereas the other group received only a saline infusion. Erythrocyte infusion increased erythrocyte volume by approximately 10%, whereas saline infusion had no effect; in addition, initially at altitude, blood oxygen content was 8% higher in erythrocyte-infused than in saline-infused subjects. The new findings regarding altitude acclimatization are summarized as follows: 1) erythrocyte volume does not change during the first 13 days and is not affected by prior exogenous expansion, 2) a modest increase in blood oxygen content does not modify erythropoietin responses, 3) plasma losses are related to vascular protein losses, and 4) exogenous erythrocyte volume expansion coincides with transient increases in plasma loss, vascular protein loss, and mean arterial pressure elevation. These findings better define human blood volume responses during altitude acclimatization.

Acclimatization↗
PubMed1996

Urinary leukotriene E4 levels increase upon exposure to hypobaric hypoxia.

STUDY OBJECTIVE: To determine whether urinary leukotriene E4 (uLTE4) levels increase upon exposure to high altitude, and also to ascertain the relationship between uLTE4 levels and symptoms of acute mountain sickness (AMS). DESIGN: Prospective, unblinded, single-factor (altitude) experimental study. SETTINGS: US Army research laboratory facilities at sea level ([SL] 50 m), 1,830 m, and 4,300 m. PARTICIPANTS: Eight healthy male subjects ranging in age from 19 to 24 years. MEASUREMENTS: uLTE4 levels and symptoms of AMS were measured at just above SL (50 m), 3 1/2 days after being transported from SL to moderate altitude (MA) (1,830 m), and 1 1/2 days after ascent from 1,830 to 4,300 m (high altitude [HA]). Symptoms of AMS were assessed using standard indexes derived from the Environmental Symptoms Questionnaire weighted toward cerebral (AMS-C) and respiratory (AMS-R) manifestations. Oxygen saturation was measured noninvasively by pulse oximetry at SL and HA. RESULTS: The mean (+/-SEM) uLTE4 levels (pg/mg creatinine) were 67.9 (+/-13.2) at SL; 82.3 (+/-5.5) at MA; and 134.8 (+/-19.4) at HA (p < 0.05 comparing HA with SL and MA). CONCLUSIONS: We conclude that uLTE4 levels increase shortly after exposure to HA even after staging for 4 days at MA. Although this study does not clearly demonstrate a relationship between uLTE4 levels and symptoms of AMS, it supports the hypothesis that leukotrienes may be involved in the pathophysiologic state of AMS.

Adult↗
PubMed1996

Effects of chemical defense clothing and individual equipment on ventilatory function and subjective reactions.

BACKGROUND: We hypothesized that the multiple layers of protective clothing (PC) of a Chemical Defense Uniform (CDU) with body armor (BA), and load bearing equipment (LBE) impose an external impedance on breathing mechanics in addition to that caused by the chemical-biological protective mask (CB mask). METHODS: We measured the effects of wearing the CDU with BA + LBE on the mechanics and pattern of breathing and subjective reactions in 15 male soldiers during rest and sustained exercise (600 W). Heat strain on each soldier was made minimal and equivalent between the battle dress uniform (BDU) and CDU configurations. RESULTS: Results from wearing the CDU were contrasted with data from wearing a physical training uniform (PTU), or BDU. At rest, the CDU decreased maximal voluntary ventilation (MVV) by 25% (p < 0.05) compared with the PTU. The CB mask alone reduced MVV 20% (p < 0.05), and the PC + BA + LBE components of the CDU contributed an additional 5% decrement (p = 0.059). The CB mask decreased maximal respiratory flows (p < 0.05), whereas the PC + BA + LBE components decreased lung volumes (p < 0.05), and potentiated the decrement of respiratory flows. Total respiratory system elastance (Ers) was increased by 16% (p < 0.05) in the CDU. During exercise, VE was comparable for both the CDU and BDU, but VT was smaller (p < 0.01) and fR greater (p < 0.05) in the CDU; a breathing pattern consistent with the increased Ers. Perceptions of anxiety, not getting enough air, not breathing the way one usually does, and not being relaxed were greater (p < 0.05) during exercise in the CDU than in the BDU. CONCLUSIONS: This study shows that some of the respiratory impairment associated with the wearing of CDU is created by the PC, BA and LBE which present a unique external constraint on the chest wall. These impairments to ventilation may provoke more aversive effects than the larger resistive loads imposed by the CB mask.

Adult↗
PubMed1995

The effect of altitude pre-acclimatization on acute mountain sickness during reexposure.

BACKGROUND: Acclimatization to high altitude appears to prevent acute mountain sickness (AMS), as evidenced by a decline in AMS symptoms as acclimatization progresses. HYPOTHESIS: We hypothesized that partial retention of acclimatization would attenuate the incidence and/or severity of AMS upon reinduction to altitude. METHODS: To test this hypothesis 6 male lowlanders returned to sea level after the acclimatizing of the 16 d at 4300 m (HA). After 8 d at sea level (PA), they were reexposed to 4300 m in a hypobaric chamber for 30 h (RA). AMS symptom severity was determined by the AMS-cerebral (AMS-C) scores calculated from the daily administration of the Environmental Symptoms Questionnaire during HA and RA. RESULTS: The mean AMS-C scores were reduced from 0.6 on HA day 1 (HA1) to 0.1 during RA (p < 0.05). Four subjects were "sick" (AMS-C > 0.7) during HA1, while only one was "sick" during RA. The % oxyhemoglobin, hemoglobin concentration and hematocrit were higher during RA compared to HA1. CONCLUSIONS: These results suggest that the retention of acclimatization after 8 d at low altitude is sufficient to attenuate AMS upon reinduction to high altitude.

Acclimatization↗
PubMed1994

Respiratory action of the canine deep pectoral muscles.

The potential respiratory action of the pectoral muscles is unclear. We studied the effect of electrically stimulated contraction of the deep pectoral muscles on intrathoracic pressure (Pes) and lung volume in 15 supine anesthetized dogs. Changes in Pes and lung volume were also compared with the forelimbs held at the animal's side and elevated 45 degrees to the horizontal plane to alter the mechanical advantage of the deep pectoral muscles. In all animals, bilateral supra-maximal stimulation of the deep pectorals produced negative changes in Pes (-5.9 +/- 0.6 cmH2O) and inspiratory changes in lung volume (324 +/- 44 ml) with the forelimbs elevated. Conversely, in all animals, stimulation of the deep pectorals with the forelimbs at the side produced positive changes in Pes (+ 2.6 +/- 0.2 cmH2O, Plt;0.001) and expiratory changes in lung volume (-113 +/- 16 ml, Plt;0.001). Furthermore, forelimb elevation increased deep pectoral muscle fiber length (mean change 39.9 +/- 7.5% of resting length, Plt;0.001) and reoriented fiber alignment with the rib cage more rostrally. These data indicate that the pectoral muscles exert a respiratory action on the rib cage. Moreover, forelimb posture affects the direction (i.e., inspiratory vs. expiratory) and magnitude of pectoral muscle mechanical action by altering muscle fiber alignment and precontraction length.

Air Pressure↗
PubMed1994

Adductor pollicis muscle fatigue during acute and chronic altitude exposure and return to sea level.

Large muscle exercise performance is impaired during acute exposure to normobaric or hypobaric hypoxia, but the effects of hypoxic conditions on fatigue of isolated smaller muscle groups per se are poorly defined. We studied how acute and chronic altitude (ALT) exposure and post-ALT return to sea level (SL) affects voluntary strength and fatigue of the adductor pollicis muscle. Eight healthy men (mean age 28 yr) were studied on five separate occasions: at SL, on days 1 (acute) and 13 (chronic) at ALT (4,300 m), and on days 1 (post 1) and 3 or 4 (post 2) at SL after 20 days of residence at ALT. On each day, maximal voluntary contractions (MVCs) of the adductor pollicis were obtained before and at the end of each minute of submaximal intermittent contractions of the adductor pollicis (50% of MVC of rested muscle, 5 s of contraction/5 s of rest) until exhaustion, defined as the inability to exert or maintain 50% of rested MVC. MVC of rested muscle did not differ among days. Time to exhaustion was shorter at acute ALT [5.1 +/- 0.5 (SE) min] than at SL (7.4 +/- 0.8 min, P < 0.05) and tended to be shorter than at chronic ALT (6.6 +/- 0.7 min, P > 0.05). Compared with acute and chronic ALT, time to exhaustion was prolonged during post 1 (9.0 +/- 1.2 min, P < 0.05) but not post 2 (6.1 +/- 0.5 min, P > 0.05). We conclude that 1) MVC of rested adductor pollicis muscle is not impaired during or after ALT exposure, 2) compared with SL conditions, acute but not chronic ALT exposure leads to a more rapid decline in adductor pollicis MVC associated with submaximal contractions, and 3) time to exhaustion is prolonged for > or = 1 day after return from ALT.

Acclimatization↗
PubMed1992

Effect of lung volume on the respiratory action of the canine pectoral muscles.

Lung volume influences the mechanical action of the primary inspiratory and expiratory muscles by affecting their precontraction length, alignment with the rib cage, and mechanical coupling to agonistic and antagonistic muscles. We have previously shown that the canine pectoral muscles exert an expiratory action on the rib cage when the forelimbs are at the torso's side and an inspiratory action when the forelimbs are held elevated. To determine the effect of lung volume on intrathoracic pressure changes produced by the canine pectoral muscles, we performed isolated bilateral supramaximal electrical stimulation of the deep pectoral and superficial pectoralis (descending and transverse heads) muscles in 15 adult supine anesthetized dogs during hyperventilation-induced apnea. Lung volume was altered by application of a negative or positive pressure (+/- 30 cmH2O) to the airway. In all animals, selective electrical stimulation of the descending, transverse, and deep pectoral muscles with the forelimbs held elevated produced negative intrathoracic pressure changes (i.e., an inspiratory action). Moreover, with the forelimbs elevated, increasing lung volume decreased both pectoral muscle fiber precontraction length and the negative intrathoracic pressure changes generated by contraction of each of these muscles. Conversely, with the forelimbs along the torso, increasing lung volume lengthened pectoral muscle precontraction length and augmented the positive intrathoracic pressure changes produced by muscle contraction (i.e., an expiratory action). These results indicate that lung volume significantly affects the length of the canine pectoral muscles and their mechanical actions on the rib cage.

Animals↗
PubMed1990

Comparison of scales used to quantitate the sense of effort to breathe in patients with chronic obstructive pulmonary disease.

Several different scaling techniques, i.e., Borg category (BC) and visual analogue (VA) scales have been used to quantitate the intensity of the respiratory sensations elicited during exercise, but their relationship is unclear. Six subjects with stable chronic obstructive lung disease (FEV1 = 1.2 +/- 0.1 SE L) simultaneously rated the sense of effort to breathe with both BC and VA scales during progressive, maximal exercise tests performed three to five times on a cycle ergometer. The VA scores correlated linearly with minute ventilation in all subjects in all trials (r = 0.98 +/- 0.01), and when converted to common units (i.e., Z scores) correlated closely with simultaneous scores obtained using the Borg scale (r = 0.99 +/- 0.01). Furthermore, VA scores varied minimally over several trials. Coefficient of variation for the maximal VA scores was 6 +/- 1%, which was similar to the variation in maximal Borg score (i.e., 3 +/- 1%). We conclude that the visual analogue scale is reproducible and correlates closely with the Borg score when scaling the sense of effort to breathe during exercise in subjects with stable chronic obstructive pulmonary disease.

Aged↗
PubMed1989

Thermoregulation during cold water immersion is unimpaired by low muscle glycogen levels.

This investigation studied the importance of muscle glycogen levels for body temperature regulation during cold stress. Physiological responses of eight euglycemic males were measured while they rested in cold (18 degrees C, stirred) water on two separate occasions. The trials followed a 3-day program of diet and exercise manipulation designed to produce either high (HMG) or low (LMG) preimmersion glycogen levels in the muscles of the legs, arms, and upper torso. Preimmersion vastus lateralis muscle glycogen concentrations were lower during the LMG trial (144 +/- 14 mmol glucose/kg dry tissue) than the HMG trial (543 +/- 53 mmol glucose/kg dry tissue). There were no significant differences between the two trials in shivering as reflected by aerobic metabolic rate or in the amount of body cooling as reflected by changes in rectal temperature during the immersions. Postimmersion muscle glycogen levels remained unchanged from preimmersion levels in both trials. Small but significant increases in plasma glucose and lactate concentration occurred during both immersions. Plasma glycerol increased during immersion in the LMG trial but not in the HMG trial. Plasma free fatty acid concentration increased during both immersion trials, but the change was apparent sooner in the LMG immersion. It was concluded that thermoregulatory responses of moderately lean and fatter individuals exposed to cold stress were not impaired by a substantial reduction in the muscle glycogen levels of several major skeletal muscle groups. Furthermore, the data suggest that, depending on the intensity of shivering, other metabolic substrates are available to enable muscle glycogen to be spared.

Adult↗
PubMed1988

Polycythemia and hydration: effects on thermoregulation and blood volume during exercise-heat stress.

We studied the effects of autologous erythrocyte infusion on thermoregulation and blood volume during exercise in the heat. Specifically, we wanted to determine whether heat-acclimated subjects, as well as hypohydrated subjects, would have a thermoregulatory advantage from acute polycythemia during exercise in the heat. Five heat-acclimated males attempted four heat stress tests (HSTs): two pre- and two postinfusion. Autologous erythrocyte infusion was accomplished with 500 ml of a NaCl-glucose-phosphate solution containing approximately 60% hematocrit. One HST, both pre- and postinfusion, was done while subjects were euhydrated, and one HST was done while subjects were hypohydrated (-5% of body wt). After 30 min of rest in a 20 degrees C antechamber, the HST consisted of a 120-min exposure (2 repeats of 15 min rest and 45 min walking) in a hot (35 degrees C, 45% relative humidity) environment. The findings concerning acute polycythemia in heat-acclimated subjects are summarized: 1) polycythemia increased (P less than 0.05) sweating rate and reduced (P less than 0.01) core temperature during exercise-heat stress for both euhydrated and hypohydrated subjects; 2) the erythrocyte infusion caused an increased (P less than 0.05) plasma volume and increased (P less than 0.01) blood volume; 3) the increased plasma volume was associated with an increased (P less than 0.05) total circulating protein mass; 4) the increased total circulating protein mass tended to better maintain plasma volume when hypohydrated; and 5) heat acclimation may increase extravascular protein mass. Therefore, it is concluded that erythrocyte infusion provides a thermoregulatory advantage during exercise in the heat for heat acclimated subjects when both euhydrated and hypohydrated.

Acclimatization↗
PubMed1988

Influence of skeletal muscle glycogen on passive rewarming after hypothermia.

To examine the influence of muscle glycogen on the thermal responses to passive rewarming subsequent to mild hypothermia, eight subjects completed two cold-water immersions (18 degrees C), followed by 75 min of passive rewarming (24 degrees C air, resting in blanket). The experiments followed several days of different exercise-diet regimens eliciting either low (LMG; 141.0 +/- 10.5 mmol.kg.dry wt-1) or normal (NMG; 526.2 +/- 44.2 mmol.kg.dry wt-1) prewarming muscle glycogen levels. Cold-water immersion was performed for 180 min or to a rectal temperature (Tre) of 35.5 degrees C. In four subjects (group A, body fat = 20 +/- 1%), postimmersion Tre was similar to preimmersion Tre for both trials (36.73 +/- 0.18 vs. 37.26 +/- 0.18 degrees C, respectively). Passive rewarming in group A resulted in an increase in Tre of only 0.13 +/- 0.08 degrees C. Conversely, initial rewarming Tre for the other four subjects (group B, body fat = 12 +/- 1%) averaged 35.50 +/- 0.05 degrees C for both trials. Rewarming increased Tre similarly in group B during both LMG (0.76 +/- 0.25 degrees C) and NMG (0.89 +/- 0.13 degrees C). Afterdrop responses, evident only in those individuals whose body core cooled during immersion (group B), were not different between LMG and NMG. These data support the contention that Tre responses during passive rewarming are related to body insulation. Furthermore these results indicate that low muscle glycogen levels do not impair rewarming time nor alter after-drop responses during passive rewarming after mild-to-moderate hypothermia.

Adult↗
PubMed1988

Respiratory and cardiovascular responses to cold stress following repeated cold water immersion.

The effects of cold acclimation (CA) on the cardiorespiratory responses to cold air and water stress tests (CST) were studied in 7 males before and after a CA program of daily 90-min cold water (18 degrees C) immersions repeated 5 times a wk for 5 consecutive wk. The CST consisted of a 90-min resting exposure to cold air (5 degrees C, 30% relative humidity) or water (18 degrees C) during which rectal temperature, oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), heart rate, cardiac output (Q), and blood pressure (BP) were periodically measured. In cold air following CA, the VO2 at 10 min was lower (P less than 0.02) post- than pre-CA, however, no differences were found in cold water. The VE increased (P less than 0.01) during CST as a function of VCO2. The CA did not affect the VE-VCO2 relationship or the pattern of breathing during CST in cold air or water. The CA had no effect on Q or (a-v) O2 difference, which both increased (P less than 0.01) during the first 45 min of CST, then remained stable. BP increased significantly during the first cold water exposure, but not during the last cold water immersion. These data indicate that CA attenuated the onset of metabolic heat production during CST in air but did not alter its ultimate magnitude or the relationships between the cardiorespiratory variables and metabolic requirements. Also, the thermoregulatory adjustments associated with CA altered the control of blood pressure during acute cold stress.

Acclimatization↗