Progress in Aerospace Sciences

Viru A., Tendzegolskis Z.

beta-Endorphin is metabolized to gamma- and alpha-endorphin. In order to evaluate endorphin metabolism during exercise, radioimmunoassay blood levels of alpha-, beta- and gamma-endorphins were recorded during exercise for 2 h on a cycling ergometer in 12 endurance-trained and 11 untrained male subjects. In untrained subjects, mild exercise (49 +/- 4% VO2max, mean +/- SD) did not show an increase in plasma beta-endorphin, while the levels of its metabolites rose. No changes were noted in the endurance-trained subjects. More intensive exercise (66 +/- 6% VO2max in untrained and 57 +/- 7% VO2max in trained subjects) resulted in an increase in beta-endorphin concentration in association with elevation of the alpha-endorphin level. While before and during exercise the beta-endorphin levels did not differ significantly between athletes and untrained subjects, the levels of gamma- and alpha-endorphins, as well as the molar ratios alpha/beta and gamma/beta, were significantly higher in untrained subjects. In conclusion, blood levels of beta-endorphin metabolites in the resting state and during exercise are dependent on previous training. In untrained subjects, mild exercise may result in accumulation of gamma- and alpha-endorphins in blood without a concomitant change in beta-endorphin level.

Fernqvist E., Linde B., Östman J., Gunnarsson R.

Nine insulin-dependent diabetics with undetectable plasma C-peptide (less than 0.05 nmol l-1) and without insulin antibodies (insulin binding to IgG less than 0.05 Ul-1) received subcutaneous injections of 10 U 125I-labelled soluble human or porcine insulin in the thigh on 2 consecutive days. Disappearance rates of 125I were monitored continuously by external counting and plasma insulin levels were determined during rest for 30 min, bicycle exercise of moderate intensity for 40 min, and 60 min recovery. Subcutaneous blood flow was measured concomitantly in the contralateral thigh by the 133Xenon clearance technique. During the initial period of rest human insulin was absorbed approximately 40% faster than its porcine analogue (first order rate constants 0.37 +/- 0.06 vs 0.27 +/- 0.06% min-1, P less than 0.05) and the increment of the area under the plasma insulin curve was greater after human than after porcine insulin (184 +/- 46 vs 112 +/- 42 mUl-1 min, P less than 0.05). Exercise enhanced the absorption rates for both 125I-insulins to 0.50 +/- 0.06 and 0.48 +/- 0.10% min-1 for human and porcine insulin, respectively (P less than 0.05). This increase was less pronounced for human compared to porcine insulin (49 +/- 19 vs 105 +/- 40%, P = 0.06). During exercise plasma insulin rose to 37 +/- 5 mUl-1 after human and 30 +/- 5 mUl-1 after porcine insulin and the areas under the plasma insulin curves were similar. During the recovery phase the absorption rates decreased slightly compared to the exercise value for both insulins. The blood glucose lowering effect was similar for the two insulins.(ABSTRACT TRUNCATED AT 250 WORDS)

Wisén A.G., Wohlfart B.

Summary. Two submaximal cycle ergometer test methods, the Åstrand nomogram test and a computerized two-point extrapolation test (Cat Eye ergociser, commercially available), were compared in order to determine agreement and repeatability of estimates of maximum oxygen consumption (VO2rnax). Twenty healthy women, divided into two groups of ten according to their age (mean 35.3 and mean 46.9), performed test-retest with each method. In both methods the VO2max was estimated from workload and the corresponding heart rate. The correlation between the VO2max using the two methods was high (r=0.85, P

Kaijser L.

Krotkiewski M., Górski J.

The levels of plasma insulin and C-peptide during exercise and subsequent recovery have been determined in obese non-diabetics, obese diabetics Type II and middle-aged female controls. It has been found that exercise reduces levels of peptides both in the control and in the obese non-diabetic group. This effect of acute exercise was found blunted in the obese diabetic group. Non-diabetic obese subjects pretreated with phentolamine showed no reduction either in plasma insulin or C-peptide levels during exercise. During the recovery, the level of plasma insulin returned promptly to the pre-exercise value in the control group but increased above the resting value in obese subjects, both non-diabetic and diabetic. In controls and non-diabetic obese the increment of C-peptide: insulin molar ratio occurred early after the onset of exercise and then returned to the resting value despite the exercise being continued. The plasma C-peptide:insulin molar ratios were reduced during the first 15 min of recovery period in obese non-diabetic subjects and returned to normal in the next 15 min. The latter may suggest that reduced insulin removal could also contribute to the increase in plasma insulin values in the obese during recovery.

Engelhart M., Kristensen J.K.

Summary. The effect of indirect cooling on finger-tip blood flow patterns were recorded in 31 patients suffering from Raynaud's phenomenon. Fifteen were suffering from generalized scleroderma with acrosclerosis (GS), and 16 from primary Raynaud's phenomenon (PR), and were compared to 13 healthy controls without cold sensitivity. Finger blood flow (FBF) was monitored by a laser Doppler flowmeter. Resting blood flow values were significantly lower in patients compared to controls. After two min of body cooling no difference could be observed in relative flow decrease between patients and controls or between PR and GS, but after 10 min of body cooling, relative flow decrease tended to be more pronounced in GS than in PR. Only in GS was the zero flow situation observed. During the resting condition, skin vessel vasomotion was observed as rhythmical variations in the blood flow of 5–10 cycles per minute. These seemed to be preserved in patients and in chronically sympathectomized patients, and could not be abolished by nerve blockade of the finger. The influence from sympathetic vasomotor fibres on FBF could be observed during cooling as irregular coarse flow fluctuations. This was observed in both patients and controls but not in the chronically sympathectomized patients and disappeared after nerve blockade of the finger. Finger temperature was measured simultaneously during body cooling, but significant changes were observed only in normals and PR. The conclusions were that (1) during body cooling, flow decrease in GS tends to be more pronounced than in PR, and only in GS could the zero flow situation be elicited; (2) influence on finger blood vessels from the sympathetic nervous system could be observed in both patients and control persons; (3) GS and PR patients seem to have preserved local vasomotion in cutaneous microvessels; (4) finger-tip temperature in sclerotic skin is an imprecise blood flow indicator.

Carroll J.F., Convertino V.A., Pollock M.L., Graves J.E., Lowenthal D.T.

The purpose of this investigation was to evaluate the effect of 6 months of exercise training on cardiovascular responses to 70 degrees head-up tilt (HUT) in the elderly. Forty-four elderly men and women (ages 60-82 years) were assigned to endurance training alone (n = 18), endurance training in combination with selected resistance exercises (n = 17), or to a non-exercising control group (n = 9). Head-up tilt testing at the start (T1) and end (T2) of 26 weeks of training consisted of 30 min of supine rest, 15 min of 70 degrees HUT, and 15 min of supine recovery. Endurance training consisted of uphill treadmill walking or stair climbing exercise 3 times per week, 30-45 min/day, at 75-85% of maximal heart rate reserve. In addition, the endurance/resistance group completed one set of 8-15 repetitions of biceps curl (BC), triceps extension (TE), and leg press, 3 times per week. After 26 weeks, increases in VO2max averaged 16.2% and 12.3% for endurance and endurance/resistance groups, respectively. In addition, the endurance/resistance group increased BC and TE strength by 25.3% and 26.1%, respectively. Results from the HUT test indicated that only the endurance group increased supine resting stroke volume (SV) and cardiac output (Q) from T1 to T2; however, SV and Q during HUT were not augmented as a result of training. Training did not affect heart rate, blood pressure, or peripheral resistance responses at rest or during HUT in any of the groups. These results suggest that 6 months of endurance training, alone or in combination with selected resistance exercises, is not detrimental to blood pressure controlling mechanisms to head-up tilt in the elderly.

Kastrup J., Rørsgaard S., Parving H.-., Lassen N.A.

Autoregulation of cerebral blood flow, i.e., the maintenance of cerebral blood flow within narrow limits during changes in arterial perfusion pressure, was studied in nine healthy control subjects and in 12 long-term Type I (insulin-dependent) diabetic patients with clinical microangiopathy. Cerebral blood flow was measured by the intravenous 133Xenon method. Mean arterial blood pressure was elevated approximately 30 mmHg by intravenous infusion of angiotensin amide II and lowered about 10 mmHg by intravenous infusion of trimethaphan camsylate. In the control subjects the flow/pressure curve was horizontal indicating perfect autoregulation. In the diabetic patients the flow/pressure curve showed a significant slope with a 1.9% change in CBF per 10 mmHg change in mean arterial blood pressure as compared to a slope value of -0.4% in the control subjects (P less than 0.05). Our results confirm the previous findings suggesting that autoregulation of cerebral blood flow is impaired in some long-term Type I diabetic patients with clinical microangiopathy (arteriolar hyalinosis).

Rehling M., Frøkiaer J., Poulsen E.U., Marqversen J., Nielsen B.V., Bacher T.

An invasive comparative study of some pharmacokinetic aspects of 99mTc-mercaptoacetyltriglycine (MAG3), 131I-orthoiodohippurate (OIH), and 125I-iothalamate (iothalamate) was performed in six pigs 0-150 min after a simultaneous single injection (SI) and during a subsequent 90 min of continuous infusion (CI). The total plasma clearance and the renal clearance of MAG3 were about 75% that of OIH. The renal clearance of MAG3 was about 2 1/2 times the glomerular filtration rate. The distribution volume of MAG3 was 71% that of iothalamate and only 47% that of OIH. There was a significant hepatic plasma clearance of MAG3 of 5.9 ml min-1 and 3.9% of the injected dose was excreted in the bile. HPLC analysis revealed that technetium was excreted in urine and bile mainly labelled to MAG3. The average red blood cell (RBC) binding after single injection/during continuous infusion was 1.0%/2.3% for MAG3, 13.5%/9.0% for OIH, and 3.1%/5.3% for iothalamate. The binding of OIH to RBC in arterial blood increased from 8% at 1 min post-injection to 21% at 150 min post-injection. The RBC binding was higher in the renal vein, indicating incomplete back diffusion from RBC to plasma. The protein binding was 90% for MAG3, 49% for OIH and 16% for iothalamate. The renal plasma extraction of MAG3 was constant but significantly smaller after SI (0.54) than during CI (0.62). Following SI, the renal plasma extraction of OIH decreased continuously from 0.85 to 0.52, 3-150 min post-injection. On the average there was no significant difference in renal plasma extraction after SI and during CI of either OIH (0.72 versus 0.77) or iothalamate (0.26 versus 0.27). It is concluded that MAG3 is preferential to OIH as a tracer for renal function studies using a single injection technique mainly due to the constant renal extraction of MAG3.

Bergström B., Lilja B., Rosberg K., Sundkvist G.

Summary. Autonomic nerve function was evaluated by deep breathing (E/I heart rate ratio) and tilt table tests (acceleration index, brake index, and blood pressures) in 56 healthy subjects in order to find reference values. The results showed that the E/I ratio, the acceleration index and the brake index fell with increasing age. There was no influence of age on the systolic and the diastolic blood pressure reactions to tilt. Age-related reference values are needed in the evaluation of autonomic neuropathy indices.

Hermanson A., Jonsson C.-., Lindblom U.

Thresholds for touch, temperature, pain and two-point discrimination were examined in 27 healthy subjects and in 36 burn patients. Three groups of injuries were examined; superficial dermal burns, which were allowed to heal spontaneously, deep dermal and subdermal burns treated by either early or late excision and skin grafting. Uninjured areas on the contralateral side served as control. In spontaneously healed superficial burns, the sensibility recovered to normal, except for touch. In deep dermal or subdermal burns all thresholds were significantly higher than in the corresponding control areas. There was no recovery beyond one month after the injury. The sensibility was better on the upper than on the lower extremities and also in deep dermal than in subdermal burns. There was no significant difference in sensibility between burns excised and grafted early or late, respectively. The results indicate that current treatment of deep dermal and subdermal burns is not followed by complete recovery of cutaneous sensation. Furthermore, even superficial burns results in incomplete recovery of touch sensibility.

Jensen-Urstad M., Hallbäck I., Sahlin K.

The influence of hypoxaemia on anaerobic energy production during arm exercise (AE) has been investigated. Six men were studied during maximal AE and during 10 min of sitting submaximal AE under both normoxic (AEN) and hypoxic (AEH, respiratory hypoxia, 12% O2) conditions. Peak pulmonary oxygen uptake (VO2) during maximal AE in normoxia and hypoxia was 2.25 +/- 0.15 and 2.18 +/- 0.14 l min-1, respectively (P < 0.05). The absolute workload was the same during submaximal AEN and AEH and corresponded to 54% of peak VO2 during normoxic maximal AE. To eliminate the potential influence of differences in catecholamine levels on the metabolic response, the submaximal experiments were performed during beta-adrenoceptor blockade. Oxygen deficit was 1.45 +/- 0.26 and 1.67 +/- 0.191 during AEN and AEH, respectively (n.s.). Oxygen extraction at steady state was lower during AEH than during AEN, and assuming a similar O2 demand this corresponds to a 14% higher muscle blood flow during AEH. At the onset of both AEN and AEH, O2 extraction (a-v O2) across the arm increased transiently above that at steady state, the increase being more pronounced during AEN than during AEH (P < 0.05). Muscle oxygenation, measured by near-infrared spectroscopy, demonstrated an initial decrease which was partially reversed as exercise proceeded. The reversal of muscle O2 desaturation was slower in all subjects during AEH (t1/2 = 2.4 +/- 0.2 min) than during AEN (t1/2 = 1.2 +/- 0.2 min; P < 0.01). After 10 min of exercise, arterial blood lactate was higher (P < 0.05) during AEH (5.5 +/- 0.2 mmol l-1) than during AEN (4.9 +/- 0.6 mmol l-1), whereas arterial plasma ammonia (NH3) was similar. The arteriovenous difference for both lactate and ammonia was similar during AEN and AEH. It is concluded that the high anaerobic energy production at the onset of AE is associated with a transient increase in O2 extraction and a transient decrease in muscle oxygenation. The effects of hypoxaemia on peak VO2, oxygen deficit and blood metabolites are less pronounced than previously described during submaximal leg exercise (LE).

Jonason T., Bäckbro B., Ringqvist I., Trella J.

Summary. The accuracy in determining the level of haemodynamically significant occlusive arterial disease (stenosis of ≥50%) in the leg by a combination of segmental blood pressure measurements and evaluation of pulses with the Doppler shift technique was assessed in 50 patients (100 legs), using angiography as the reference method. For aorto-iliac disease the sensitivity was 72%, the specificity 97% and the diagnostic accuracy 87%. For femoro-popliteal disease the corresponding figures were 87%, 78% and 85%, respectively. The accuracy of a positive diagnosis was 93% for both levels. Similar results were obtained for combined aorto-iliac and femoro-popliteal disease. The accuracy in detecting calf disease was poor.

Töyry J., Mäntysaari M., Hartikainen J., Länsimies E.

We examined the reproducibility of day-to-day variability in cardiovascular autonomic nervous function parameters (classical clinical tests and domain analysis of heart rate variability) in four healthy men during a period of 1 working week. The results did not show any significant difference in any of the parameters over the five repeated measurements. The maximum-minimum difference as percentage of the mean was under 15% for expiration to inspiration (E/I) ratio, Valsalva ratio, tachycardia ratio, 30/15 ratio, acceleration index and brake index; about 45% for baroreflex sensitivity for systolic and diastolic blood pressure and for root mean square difference (RMSSD) of successive R-R intervals; about 65-85% for low and high frequency bands, total power and medium to high frequency ratio; and about 125% for medium frequency band. The intraclass correlation coefficient (ICC) values showed that the agreement for classical autonomic parameters (except for brake index) was good. ICC for RMSSD, baroreflex sensitivity for systolic blood pressure and the spectral estimates of heart rate variation were less good. Coefficient of variation (CV) was 4% for E/I ratio, 2% for 30/15 ratio, 6% for Valsalva, 3% for tachycardia ratio, 4% for acceleration index and 5% for brake index. CV for baroreflex sensitivity and for RMSSD was about 20%. It is concluded that the variation in baroreflex sensitivity is clearly larger than in the classical autonomic nervous function parameters. One-minute fixed pace breathing period seems to be too short to allow reproducible measurement of RMSSD and the spectral parameters of heart rate variation. Learning effect could be excluded.