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Biomedical subjects

A Veicsteinas

Publications and source records attributed to A Veicsteinas.

At least 55 records · Page 3Linked to original sources
PubMed1989

Conductive and convective heat flows of exercising humans in cold water.

The apparent conductance (Kss, in W.m-2.degrees C-1) of a given region of superficial shell (on the thigh, fat + skin) was determined on four nonsweating and nonshivering subjects, resting and exercising (200 W) in water [water temperature (Tw) 22-23 degrees C] Kss = Hss/(Tsf-Tsk) where Hss is the skin-to-water heat flow directly measured by heat flow transducers and Tsf and Tsk are the temperatures of the subcutaneous fat at a known depth below the skin surface and of the skin surface, respectively. The convective heat flow (qc) through the superficial shell was then estimated as qc = (Tsf - Tsk).(Kss - Kss,min), assuming that at rest Kss was minimal (Kss,min) and resting qc = 0. The duration of immersion was set to allow rectal temperature (Tre) to reach approximately 37 degrees C at the end of rest and approximately 38 degrees C at the end of exercise. Except at the highest Tw used, Kss at the start of exercise was always Kss,min and averaged 51 W.m-2.degrees C-1 (range 33-57 W.m-2.degrees C-1) across subjects, and qc was zero. At the end of exercise at the highest Tw used for each subject, Kss averaged 97 W.m-2.degrees C-1 (range 77-108 W.m-2.degrees C-1) and qc averaged 53% (range 48-61%) of Hss (mean Hss = 233 W.m-2).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Plasma catecholamines and heart rate at the beginning of muscular exercise in man.

The relationship between the time course of heart rate and venous blood norepinephrine (NE) and epinephrine (E) concentrations was studied in 7 sedentary young men before and during 3 bicycle exercises of 5 min each (respectively 23 +/- 2.8%, 45 +/- 2.6% and 65 +/- 2.4% VO2max, mean +/- SE). During the low level exercise the change in heart rate is monoexponential (tau = 5.7 +/- 1.2 s) and no increment above the resting level of NE (delta NE) or of E (delta E) occurs. At the medium and highest intensity of exercise: a) the change in heart rate is biexponential, tau for the fast and the slow component averaging about 3 and 80 s respectively; b) delta NE (but not delta E) increases continuously with time of exercise; c) at the 5th min of exercise heart rate increments are related to delta NE; d) between 20 s and 5 min, at corresponding sampling times, the heart rate of the slow component is linearly related to delta NE. At exercise levels higher than 33% VO2max the increase in heart rate described by the slow component of the biexponential kinetic could be due to an augmented sympathetic activity revealed by increased NE blood levels.

Adult↗
PubMed1988

Spectral analysis of muscular sound at low and high contraction level.

The activated muscle generates a low frequency rumbling noise, which is known as the Sound-MyoGram (SMG). Spectral analysis of the SMG is carried out in this work, in order to: (i) check the adequacy of both the Fast Fourier Transform (FFT) and the Maximum Entropy Spectrum Estimation (MESE). Because it is a well known technique, the FFT method is only briefly described, while the philosophy of the MESE method is given in more detail and completed with a description of the recursive algorithm; (ii) select a frequency parameter suitable to describe the SMG. For this purpose two well-defined physiological conditions (20% and 80% Maximal Voluntary Contraction) have been adopted in order to provide a safe reference for the interpretation of the findings. The results show that: (a) both FFT and MESE are adequate to estimate the SMG Power Spectrum; (b) both the mean and the median frequency are suitable parameters, the mean frequency being the more favourable one; (c) the SMG Power Spectrum is a promising tool to study the muscle activation modalities.

Adult↗
PubMed1988

Regional heat flows of resting and exercising men immersed in cool water.

Trunk (HT), limb (HL), and whole-body (HDIR = HT + HL + Hforehead) skin-to-water heat flows were measured by heat flow transducers on nine men immersed head out in water at critical temperature (TCW = 30 +/- 2 degrees C) and below [overall water temperature (TW) range = 22-32 degrees C] after up to 3 h at rest and exercise. Body heat flow was also determined indirectly (HM) from metabolic rate corrected for changes in heat stores. At rest at TCW [O2 uptake (VO2) = 0.33 +/- 0.07 l/min, n = 7], HT = 52.3 +/- 14.2 (SD) W, HL = 56.4 +/- 14.6 W, HDIR = 120 +/- 27 W, and HM = 111 +/- 29 W (significantly different from HDIR). TW markedly affected HDIR but only slightly affected HM (n = 22 experiments at TW different from TCW plus 7 experiments at TCW). During light exercise (3 MET) at TCW (VO2 = 1.06 +/- 0.26 l/min, n = 9), HT = 122 +/- 43 W, HL = 130 +/- 27 W, HDIR = 285 +/- 69 W, and HM = 260 +/- 60 W. During severe exercise (7 MET) at TCW (VO2 = 2.27 +/- 0.50 l/min, n = 4), HT = 226 +/- 100 W, HL = 262 +/- 61 W, HDIR = 517 +/- 148 W, and HM = 496 +/- 98 W. Lowering TW at 7-MET exercise (n = 9, plus 4 at TCW) had no effect on HDIR and HM. In conclusion, resting HL and HT are equal. At TW less than TCW at rest, HDIR greater than HM, showing that unexpectedly the shell was still cooling. During exercise, HL increases more than HT but less than expected from the heat production of the working limbs. Therefore some heat produced by the limbs is probably transported by blood to the trunk. During heavy exercise, HDIR is constant at all considered TW; apparently it is regulated by some thermally dependent mechanism, such as a progressive cutaneous vasodilation occurring as TW increases.

Body Temperature Regulation↗
PubMed1986

Physiological profile of world-class high-altitude climbers.

The functional characteristics of six world-class high-altitude mountaineers were assessed 2-12 mo after the last high-altitude climb. Each climber on one or several occasions had reached altitudes of 8,500 m or above without supplementary O2. Static and dynamic lung volumes and right and left echocardiographic measurements were found to be within normal limits of sedentary controls (SC). Muscle fiber distribution was 70% type I, 22% type IIa, and 7% type IIb. Mean muscle fiber cross-sectional area was significantly smaller than that of SC (-15%) and of long-distance runners (LDR, -51%). The number of capillaries per unit cross-sectional area was significantly greater than that of SC (+ 40%). Total mitochondrial volume was not significantly different from that of SC, but its subsarcolemmal component was equal to that of LDR. Average maximal O2 consumption was 60 +/- 6 ml X kg-1 X min-1, which is between the values of SC and LDR. Average maximal anaerobic power was 28 +/- 2.5 W X kg-1, which is equal to that of SC and 40% lower that that of competitive high jumpers. All subjects were characterized by resting hyperventilation both in normoxia and in moderate (inspired O2 partial pressure = 77 Torr) hypoxia resulting in higher oxyhemoglobin saturation levels in hypoxia. The ventilatory response to four tidal volumes of pure O2 was similar to that of SC. It is concluded that elite high-altitude climbers do not have physiological adaptations to high altitude that justify their unique performance.

Adaptation, Physiological↗
PubMed1985

Ventilatory response during incremental exercise tests in weight lifters and endurance cyclists.

The effect of a progressively increasing work rate (15 W X min-1) up to exhaustion on the time course of O2 uptake (VO2), ventilation (VE) and heart rate (HR) has been studied in weight lifters (WL) in comparison to endurance cyclists (Cycl) and sedentary controls (Sed). VO2 and VE were measured as average value of 30-s intervals by a semiautomatic open circuit method. VO2max was 2.55 +/- 0.33; 4.29 +/- 0.53 and 2.86 +/- 0.19 l X min-1 in WL, Cycl and Sed respectively. With time and work rate, while VO2 and HR increased linearly, VE changed its slope at two levels. The 1st VE change occurred at a work load corresponding to a mean (+/- SD) VO2 of 1.50 +/- 0.26; 1.93 +/- 0.34; and 1.23 +/- 0.14 l X min-1 in WL, Cycl, and Sed respectively. VO2 values corresponding to the second VE change of slope were 2.18 +/- 0.32 in WL; 3.48 +/- 0.53 in Cycl and 2.17 +/- 0.28 l X min-1 in Sed. The first change of slope might be the consequence of the different readjustment of VO2 on-response and hence of early lactate in the different subjects. The second change seems to be comparable to the conventional anaerobic threshold and is achieved in all subjects when VE vs time slope is 7-10 l X min-1/min of exercise.

Adult↗
PubMed1984

Energy cost of and energy sources for alpine skiing in top athletes.

O2 uptake (VO2) during exercise and at 2 min of the recovery along with blood lactate concentration 5 min after exercise were measured in an all-out special slalom (SS) and giant slalom (GS) performed by eight top male athletes and five controls in a field study. Heart rate (HR) was continuously monitored before, during, and after each task. On the basis of an energy equivalent of 3.15 ml O2 X kg body wt-1 for 1 mmol X 1-1 lactate accumulation and the assumption that the amount of O2 consumed in recovery is used to reconstitute approximately phosphates used during the exercise, the total energy cost (delta VO2 tot) could be calculated and subdivided into aerobic, lactic, and alactic fractions. In top athletes, delta VO2 tot was equal during SS and GS [7.28 +/- 1.14 (SD) and 7.47 +/- 0.89 liters for about 55- and 70-s performances, respectively]. When referred to time, the O2 expenditure rate was 2 and 1.6 times VO2max in SS and GS, respectively. In SS and GS, the energy sources were about 40% aerobic, 20% alactic , and 40% lactic metabolism. In control skiers, delta VO2 tot of GS was 6.12 +/- 1.45 liters for 77 s, amounting to about 1.3 VO2max, with the contribution of the different energy sources being roughly the same as in top skiers. HR reached maximal values in 30-40 s in all subjects for all conditions.

Adult↗
PubMed1984

Blood O2 affinity and maximal O2 consumption in elite bicycle racers.

The PO2 at which hemoglobin is half-saturated with O2 (P50) at 37 degrees C, PCO2 = 42 Torr, measured pH and 2,3-diphosphoglycerate-to-hemoglobin concentration ratio ( [2,3-DPG]/[Hb]) values, Hill's coefficient (n) at rest, and maximal O2 consumption (VO2max) were determined in 11 world-class professional bicycle racers off-season (control, C), after 3 mo of 3 h daily training (preseason, PrS), and after additional 6 mo of competitions (competitive season, CoS). The results indicate that the P50 observed in trained athletes was the same as that of a comparable group of sedentary subjects (Sed) under the same conditions of pH, PCO2, and [2,3-DPG]/[Hb] and was similar to that obtained after "normalization" in respect to pH and the [2,3-DPG]/[Hb]; [2,3-DPG]/[Hb] increased as a function of training from 0.72 to 0.95 (P less than 0.001); the slope of the central portion of the O2 equilibrium curve (OEC) was nearly unaffected by endurance training as indicated by the n value (NCoS = 2.70 +/- 0.08; nSed = 2.65 +/- 0.08); and VO2max increased in the course of training 7 and 9% (P less than 0.001), respectively, when expressed in absolute units or per kilogram body weight. The VO2max predicted on the basis of a computer simulation does not increase significantly as a consequence of the measured rise in [2,3-DPG]. Therefore, the observed increase of VO2max cannot be explained with adaptive changes of the OEC. The present results differ from previous findings reported in other types of athletes.

2,3-Diphosphoglycerate↗
PubMed1982

Cardiac output and cardiac load during isometric exercise in man.

Cardiac output, heart rate, arterial pressure and indirect left ventricular oxygen consumption have been measured in three subjects during isometric contractions (50-170 kg) of the plantar flexors until fatigue was reached and during walking on a treadmill. Cardiac output was linearly related to VO2 for both exercises. However, for the same VO2, Q was four times higher during isometric effort than during walking. In the last 15 s of static tasks, HR was linearly increasing to VO2 and AP reached values of 160 and 125 Torr (systolic and diastolic respectively) independently of VO2. For comparable VO2 in static and isotonic exercises myocardial O2 uptake was doubled during isometric rather than during the isotonic exercise.

Blood Pressure↗
PubMed1982

[Kinetics of adjustment of cardiac output to muscular exertion].

The kinetics of oxygen uptake (VO2), cardiac output (Q), and heart rate (HR) were studied in three healthy male subjects during onset of exercises up to 750 kpm/min. VO2 was measured on a single breath basis, Q by CO2-N2 rebreathing method at 30" intervals from time 0 to 6 min of exercise, and HR beat by beat. In the transition from rest to exercise, the increase of Q and VO2 follows a single exponential function, while h. r. a double exponential. Average half times of Q and VO2 during the onset of exercise are about 18" and 26" respectively. Q changes seem to anticipate VO2 changes at the first 15-45 s of exercise, while thereafter a proportional increase is observed. This non-linear increase of Q to VO2 at the beginning of exercise may presumably be due to a neurogenic control of h.r. and hence of Q from receptors at muscular level.

Cardiac Output↗
PubMed1982

Ventilatory work during exercise at high altitude.

Oxygen consumption, ventilation, and dynamic respiratory work were measured in three male subjects during cycling at 122 and 3500 m above sea level (ASL). At a given ventilation the dynamic respiratory work was 20% less at 3500 m ASL; this change was due to a decrease of airway resistance. At a given submaximal exercise intensity, the respiratory work was significantly higher at 3500 m ASL (+ 140%-180%); hence, the increase of ventilation was not compensated for by the decrease of airway resistance. At VO2max the respiratory work was predicted to reach its maximal value at 5800 m ASL where it was 30% higher than at sea level.

Airway Resistance↗
PubMed1982

Thermal insulation and shivering threshold in Greek sponge divers.

Sublingual temperature (Tor), average skin temperature (Tsk), and skin heat flow (Hsk) were determined in a field study for six Greek sponge divers and seven nondiving controls during head-out immersions at water temperature of 21 degrees C. Wetsuits kept Tsk at 22-28 degrees C for 1-3 h until Tor fell to 36.5-35.5 degrees C and violent shivering [metabolic rate (M) = 100-150 W . m-2] ended the test. At a steady Tsk, immediately before shivering, overall tissue insulation (It), calculated as (Tor--Tsk)/Hsk, was linearly related to mean subcutaneous fat thickness (MFT) in both groups without statistical difference between them. The onset of shivering, as detected by a sharp increase of M, occurred at the same Tor for a Tsk of about 26 degrees C, and the relationship of M vs. Tor (i.e., metabolic sensitivity) was the same for both groups. Contrary to other groups accustomed to diving in cold water, the use of a wetsuit for a long time has evidently prevented cold adaptation in these divers.

Adipose Tissue↗
PubMed1982

Superficial shell insulation in resting and exercising men in cold water.

From measurements of subcutaneous fat temperature (Tsf) at known depths below the surface, skin surface temperature (Tsk), and direct skin heat flux (H), the superficial shell isulation (Iss) of the thigh (fat + skin) was calculated as Iss (degrees C.m2.w-1) = (Tsf - Tsk)/H in nine male subjects immersed head out in a well-stirred water bath. Also, at critical water temperature (CWT = 28-33 degrees C), eight of the subjects rested for 3 h, enabling overall maximal tissue insulation (It,max) to be calculated as It,max (degrees C.m2.W-1) = (Tre - Tw)/(0.92 M +/- delta S), where Tre is rectal temperature, Tw is water temperature, M is metabolic rate, and s is loss or gain of body heat. Five subjects performed up to 2 h of mild leg cycling, preceded and followed by 60 min of rest, and both thigh Iss and overall It were measured during exercise. Iss increased from minimal values in Tw greater than 33 degrees C to maximal values (Iss,max) at CWT or below. Iss,max was linearly related to tissue thickness (d) in millimeters of fat plus skin, Iss,max (degrees C.m2.W-1) = 0.0048d-0.0052; r = 0.95, n = 37, and was not influenced by leg exercise up to a metabolic rate of 150 W.m-2 in CWT despite large increases in Tsf and H and large decreases in overall It. The slope of Iss,max vs. depth, 0.0048 degrees C.m2.W-1.mm-1, is almost identical to thermal resistivity of fat in vitro, suggesting that the superficial shell is unperfused in CWT at rest or during mild exercise. When maximal superficial shell insulation (It,ss,max) for the whole body was calculated with allowance for differing fat thicknesses and surface areas of body regions, it could account for only 10-15% of overall It,max at rest and 35-40% of overall It in mild exercise. We suggest that the poorly perfused muscle shell plays a more important role as a defense against cooling at CWT than does the superficial shell (fat + skin), particularly at rest.

Adipose Tissue↗
PubMed1980

A simple method for measuring oxygen uptake on a single breath basis.

A simple method for calculating breath by breath O2 uptake by the conventional open circuit method is described. Each expiratory volume is collected in a collapsible bag (4 1 capacity) surrounded by a rigid box connected to a spirometer. A system of tubes with two solenoid valves operated by a manual switch allows the collection of air into the bag, during expiration, and its emptying by a vacuum pump during inspiration, respectively. The sampling line of a fast responding O2 and CO2 analyzer, together with temperature and pressure probes are inserted into the tube connecting the bag to the vacuum. The expired volume is therefore recorded (by the spirometer output) during expiration and its composition analyzed during the immediately following inspiratory phase, thus allowing gas exchange measurements to be performed on each single breath. VO2 measured by this method at steady state over periods of about 1 min yields substantially the same values as obtained by standard open circuit method (average ratio = 1.01). Ventilations up to 150 l/min (ATPS) and respiratory rates up to 60/min can be easily followed. The simplicity of VO2 calculation, and the very limited dead space of the system (about 70 ml, downstream the expiratory valve), make this method particularly suitable for determining VO2 kinetics at the onset and offset of exercise.

Anesthesia↗
PubMed1979

Oxygen affinity of blood in altitude Sherpas.

Oxygen equilibrium curves on blood within 6 h from sampling have been estimated from polarographic measurements of oxyhemoglobin concentration, in 13 male 14- to 50-yr old Sherpas residing at 3,850 m above sea level (Kumjung, Nepal). In samples with red blood cell counts = 4.7 +/- 0.8 (SD) x 10(6)/mm3, total hemoglobin concentration [Hb] = 17.0 +/- 1.9 g/dl, and hematocrit = 53.3 +/- 5.0, the mean oxygen half-saturation of hemoglobin (P50) (pH = 7.4 and PCO2 = 40 Torr) was 27.3 +/- 1.8 Torr. The P50 of altitude Sherpas was not significantly different from that of acclimatized lowlanders (28.2 +/- 1.3; n = 7), sea-level Caucasian residents (26.5 +/- 1.0; n = 17), and Sherpas at sea level (27.1; n = 3). The 2,3-diphosphoglyceric acid-to-hemoglobin concentration ratio ([2,3-DPG]/[Hb]) in altitude Sherpas was 1.22 +/- 0.03, the same as that of acclimatized Caucasians (1.22 +/- 0.10). The Bohr effect measured for the blood of one altitude Sherpas by the ratio deltalog P50/deltapH was -0.32 and -0.45 at PCO2 levels of 40 and 20 Torr, respectively. These values are not significantly different from those found in Caucasians at sea level where deltalog P50/deltalpH was -0.35 and -0.42, respectively. It is concluded that the P50 in native highlanders is not significantly different from that observed in sea-level dwellers. [2,3-DPG]/[Hb] at altitude, both in natives and in newcomers, is 20% higher than in sea-level residents.

Adaptation, Physiological↗
PubMed1979

Energy cost of walking with lesions of the foot.

The oxygen consumption during walking was measured in patients affected by chronic lesions of the foot. Only subjects with rigidity of the talocalcaneal joint showed increased oxygen consumption, which reached 5 to 20 per cent above normal. They also showed an increased step frequency, probably as a compensatory mechanism to reduce the mechanical work performed during each step.

Adolescent↗
PubMed1978

The syndrome of carnitine deficiency: morphological and metabolic correlations in two cases.

Two cases of systemic carnitine deficiency are described. In both patients, carnitine concentration was lower than normal in serum and muscle tissue. In the first case, the illness began at age 35; the clinical manifestations were only muscular. In the second case, the illness began in childhood; there were intermittent episodes of hepatic enlargement and coma. An excessive lipid content was present in muscle tissue, especially in type 1 fibers, of both cases, and in the liver of the second patient. Ultrastructural studies of muscle tissue revealed important changes of mitochondria. During muscular exercise, aerobic and anaerobic metabolism were investigated. For a given relative work intensity, these patients showed abnormally high blood lactic acid concentration and lactic acid/pyruvic acid ratios. These data, together with the morphological alterations observed in mitochondria, suggest an impaired function of the respiratory chain, leading to a shift of the red/ox potential of the tissue towards a non reduced state.

Adult↗