Effects of skin pressure by clothing on digestion and orocecal transit time of food

In order to reveal the influence of clothing skin pressure on digestion of food through the gastrointestinal tract, we examined the absorption of dietary carbohydrate and orocecal transit time of a test meal by means of a breath hydrogen test on 7 healthy young women. In this experiment, we collected breath samples from the participants wearing loose-fitting experimental garment on the second day of the experiment and from the same participants but wearing an additional tight-fitting girdle on the following day for 16 hours and 9 hours, respectively. Skin pressure applied by a girdle on participant's waist, abdomen and hip region was 15.5 +/- 0.4 mmHg (mean +/- SE), 11.0 +/- 0.2 mmHg, and 13.6 +/- 0.6 mmHg, respectively, and the values were 2-3 times larger than those of the experimental garment. The hydrogen concentration vs. time curve showed that breath hydrogen levels at its peaks (15:00, 15:30, 16:00, 16:30, and 17:00 hr) on the third day of the experiment were significantly higher than those of the corresponding time on the second day (p < 0.05 at 17:00 and 15:00, p < 0.01 at 15:00, 16:00 and 16:30). Consequently, significantly pronounced breath hydrogen excretion was observed under the "pressure" clothing condition (p < 0.01). On the other hand, the transit time of the test meal for the subjects wearing a girdle did not differ significantly from that for the subjects wearing the garment of less pressure (270 +/- 18 minutes and 263 +/- 21 minutes, respectively). These results indicate that the clothing skin pressure has an inhibitory effect on the absorption of dietary carbohydrate in the small intestine, but no effect on the orocecal transit time of a meal.     

Effect of skin pressure by clothing on small bowel transit time

We examined the effect of increased skin pressure from tight clothing on small bowel transit time by means of the breath hydrogen test, using milk that contained lactulose as an additional indigestible disaccharide, which is used as a test meal after overnight fasting. In this experiment, we measured the small bowel transit time from 9 healthy and non-constipated female subjects with two different skin pressures that were applied by loose-fitting experimental garment or an additional tight-fitting girdle on two consecutive days. The skin pressure of the latter condition was 8-9 mmHg higher than that of the former one on the participants' waist, abdomen and hip region. The experimental order of the two skin pressure conditions was counterbalanced. As a result, the small bowel transit time obtained with and without girdle did not differ significantly (165.0 +/- 26.0 minutes for less skin pressure condition and 173.3 +/- 26.8 minutes for more skin pressure condition, n = 9, p = 0.43). This result indicated that the skin pressure from clothing has no effect on the passage rate of food through the small intestine.     

The effects of skin pressure by clothing on circadian rhythms of core temperature and salivary melatonin

The present experiment investigated the effects of skin pressure by foundation garments (girdle and brassiere) on the circadian rhythms of core temperature and salivary melatonin. Ten healthy females (18-23 years) maintained regular sleep-wake cycles for a week prior to participation in the experiment. The experiments were performed from June to August 1999 using a bioclimatic chamber controlled at 26.5 degrees C +/- 0.2 degrees C and 62% +/- 3% RH. Ambient light intensity was controlled at 500 lux from 07:30 to 17:30, 100 lux from 17:30 to 19:30, 20 lux from 19:30 to 23:30; there was total darkness from 23:30 to 07:30. The experiment lasted for 58h over three nights. The participants arose at 07:30 on the first full day and retired at 23:30, adhering to a set schedule for 24h, but without wearing foundation garments. For the final 24h of the second full day, the subjects wore foundation garments. Rectal and leg skin temperatures were measured continuously throughout the experiment. Saliva and urine were collected every 4h for the analysis of melatonin and catecholamines, respectively. Skin pressure applied by the foundation garments was in the range 11-17 gf/cm2 at the regions of the abdomen, hip, chest, and back. The main results were as follows: (1) Rectal temperatures were significantly higher throughout the day and night when wearing foundation garments. (2) The nocturnal level of salivary melatonin measured at 03:30 was 115.2 +/- 40.4 pg/mL (mean +/- SEM, N = 10) without and 51.3 +/- 18.4 pg/mL (mean +/- SEM, N = 10) with foundation garments. (3) Mean urinary noradrenaline excretion was significantly lower throughout the day and night when wearing foundation garments (p < .05), but mean urinary adrenaline excretion was not different. The results suggest that skin pressure by clothing could markedly suppress the nocturnal elevation of salivary melatonin, resulting in an increase of rectal temperature.     

Effects of skin pressure applied by cuffs on resting salivary secretion

The effects of pressure applied by cuffs to the abdomen, thighs and legs on resting salivary flow rate and digestive function of saliva were investigated in 9 healthy female students, aged 18 to 33 yrs (Experiment I) in a climatic chamber (Ta: 28 degrees C, RH: 50%). Each participant changed from street clothing into loose-fitting experimental garments so as to avoid any skin pressure on the body, and sat calmly in a reclining chair throughout the experimental period (195 min). After 90 min (FREE period), the physiological effects of skin pressure applied by their own clothing disappeared, and skin pressure was applied for the next 60 min to the abdomen (40 mmHg) and thighs (40 mmHg) then to the legs (60 mmHg) by the use of air-inflated cuffs (PRESSURE period). During the next 45 min, the skin pressure was again removed by letting the air of the cuffs out (FREE' period). The resting salivary flow rate was significantly suppressed while the skin pressure was applied by the cuffs. The digestive time for starch investigated in terms of the iodine starch reaction was longer with the skin pressure than without. The concentration of amylase measured in 20 female participants aged 21 to 23 yrs, decreased with skin pressure applied by the usage of the rubber tape (Experiment II). These results suggest that the pressure applied to the body can influence the digestive response by decreasing the amount of saliva via the autonomic nervous system.     

Field studies on inhibitory influence of skin pressure exerted by a body compensatory brassiere on the amount of feces

The present experiment investigated the effects of skin pressure produced by a body compensatory brassiere on defecation activity. Seven healthy females (11-41 yrs) volunteered as participants, being free of medication and constipation. The experiment lasted 3 weeks. The participants did not wear the body compensatory brassiere for the first week, wore it during waking hours for the second week, and again did not wear it for the third week. Whenever they desired to defecate, they did so and then weighted the amount of feces immediately by themselves. Eating times, daily amounts of foods and drinks, their menu, work intensity and its duration, retiring and rising time were controlled to be as similar as possible from day to day. The main finding was that the amount of feces was significantly smaller during the second week (wearing the body compensatory brassiere) than the first and third weeks (not wearing the body compensatory brassiere). These observations are discussed in terms of the suppression of the parasympathetic nervous system and intestine motility, and the delayed transit time in the large intestine.     

Utilizing intraluminal pressure differences to predict esophageal bolus flow dynamics

Successful esophageal emptying depends on the generation of a sustained intrabolus pressure (IBP) sufficient to overcome esophagogastric junction (EGJ) obstruction. Our aim was to develop a manometric analysis paradigm that describes the bolus driving pressure difference and the flow permissive time for esophageal bolus transit. Twenty normal subjects were studied with a 36-channel manometry assembly (1-cm spacing) during two 5- and one 10-ml barium swallows and concurrent fluoroscopy. Bolus domain pressure plots were generated by plotting bolus domain pressure (BDP) and EGJ relaxation pressure. BDP was defined as the pressure midway between the peristaltic ramp-up and the proximal margin of the EGJ. The flow permissive time was defined as the period where the BDP was > or = EGJ relaxation pressure. The mean BDP was 11.7 +/- 1.0 mmHg (SE), and the mean flow permissive time was 3.9 +/- 0.4 s for 5-ml swallows in normal controls. The mean BDP difference during flow was 4.0 +/- 1.0 mmHg. There was no significant difference in the fluoroscopic transit time and the flow permissive time calculated from the BDP plots (5 ml: fluoroscopy 3.4 +/- 0.2 s; BDP 3.9 +/- 0.4 s, P > 0.05). BDP plots provide a reliable measurement of IBP and its relationship with EGJ relaxation. The time available for flow can be readily delineated from this analysis, and the driving pressure responsible for flow can be accurately described and quantified. This may help predict abnormal bolus transit and the underlying mechanical properties of the EGJ.     

Role of nitric oxide in mediating cardiovascular alterations accompanying heart failure in rats

The present study was designed to evaluate the role of endothelial NO in the hemodynamics and vascular changes that occur in heart failure following myocardial infarction in rats. Left ventricular systolic pressure (LVSP), mean blood pressure (MBP), aortic morphology (media thickness) and reactivity were evaluated in rats with coronary artery ligation (heart failure, HF) or sham operation (SO) untreated or treated for four weeks with either a low dose of NG-nitro-L-arginine methyl ester (L-NAME, 6 mg.kg(-1).day(-1)) or L-arginine (1.5 g.kg(-1).day(-1)). In rats with HF LVSP (HF = 111 +/- 8 mmHg; SO = 143 +/- 6 mmHg, p < 0.05), MBP (HF = 98 +/- 8 mmHg; SO = 127 +/- 6 mmHg, p < 0.05) and aortic media thickness (HF = 68 +/- 6 microm; SO = 75 +/- 2 microm, p < 0.05) were significantly reduced. The contractile response to phenylephrine and the endothelium-independent relaxation to sodium nitroprusside were similar in HF and SO aortas, but the sensitivity (pD2) to acetylcholine (HF = 7.5 +/- 0.06; SO = 7.1 +/- 0.08, p < 0.05) was significantly increased in HF aortas, indicating an enhanced basal NO release. Treatment with L-NAME (LN) reversed the effects of HF on LVSP (HF-LN = 143 +/- 9 mmHg, p < 0.05 vs. HF), MBP (HF-LN = 128 +/- 8 mmHg, p < 0.05 vs. HF), sensitivity to acetylcholine (HF-LN = 6.9 +/- 0.10, p < 0.05 vs. HF) and aortic media thickness (HF-LN = 79 +/- 2 microm, p < 0.05 vs. HF), without changing these parameters in SO rats. L-NAME also selectively increased the maximal response to phenylephrine in HF aortas (HF-LN = 2.4 +/- 0.20 g; HF = 1.6 +/- 0.17 g, p < 0.05). L-arginine (LA) did not change the effects of HF on LSVP, MBP or aortic media thickness, but it reduced the sensitivity to phenylephrine in aortas from SO rats (SO-LA = 6.5 +/- 0.12; SO = 7.0 +/- 0.09, p < 0.05). Taken together, these results suggest an important role for endothelial NO in mediating the reduced vascular growth, myocardial dysfunction and hypotension in rats with HF.     

Effects of diabetes and gender on mechanical properties of the arterial system in rats: aortic impedance analysis

We determined the effects of diabetes and gender on the physical properties of the vasculature in streptozotocin (STZ)-treated rats based on the aortic input impedance analysis. Rats given STZ 65 mg/kg i.v. were compared with untreated age-matched controls. Pulsatile aortic pressure and flow signals were measured and were then subjected to Fourier transformation for the analysis of aortic input impedance. Wave transit time was determined using the impulse response function of the filtered aortic input impedance spectra. Male but not female diabetic rats exhibited an increase in cardiac output in the absence of any significant changes in arterial blood pressure, resulting in a decline in total peripheral resistance. However, in each gender group, diabetes contributed to an increase in wave reflection factor, from 0.47 +/- 0.04 to 0.84 +/- 0.03 in males and from 0.46 +/- 0.03 to 0.81 +/- 0.03 in females. Diabetic rats had reduced wave transit time, at 18.82 +/- 0.60 vs 21.34 +/- 0.51 msec in males and at 19.63 +/- 0.37 vs 22.74 +/- 0.57 msec in females. Changes in wave transit time and reflection factor indicate that diabetes can modify the timing and magnitude of the wave reflection in the rat arterial system. Meanwhile, diabetes produced a fall in aortic characteristic impedance from 0.023 +/- 0.002 to 0.009 +/- 0.001 mmHg/min/kg/ml in males and from 0.028 +/- 0.002 to 0.014 +/- 0.001 mmHg/min/kg/ml in females. With unaltered aortic pressure, both the diminished aortic characteristic impedance and wave transit time suggest that the muscle inactivation in diabetes may occur in aortas and large arteries and may cause a detriment to the aortic distensibility in rats with either sex. We conclude that only rats with male gender diabetes produce a detriment to the physical properties of the resistance arterioles. In spite of male or female gender, diabetes decreases the aortic distensibility and impairs the wave reflection phenomenon in the rat arterial system.     

Modulation of arterial baroreflex control of heart rate by skin cooling and heating in humans.

The purpose of this study was to examine the effects of skin cooling and heating on the heart rate (HR) control by the arterial baroreflex in humans. The subjects were 15 healthy men who underwent whole body thermal stress (esophageal temperatures, approximately 36.8 and approximately 37.0 degrees C; mean skin temperatures, approximately 26.4 and approximately 37.7 degrees C, in skin cooling and heating, respectively) produced by a cool or hot water-perfused suit during supine rest. The overall arterial baroreflex sensitivity in the HR control was calculated from spontaneous changes in beat-to-beat arterial pressure and HR during normothermic control and thermal stress periods. The carotid baroreflex sensitivity was evaluated from the maximum slope of the HR response to changes in carotid distending pressure, calculated as mean arterial pressure minus neck pressure. The overall arterial baroreflex sensitivity at existing arterial pressure increased during cooling (-1.32 +/- 0.25 vs. -2.13 +/- 0.20 beats. min(-1). mmHg(-1) in the control and cooling periods, respectively, P < 0.05), whereas it did not change significantly during heating (-1.39 +/- 0. 23 vs. -1.40 +/- 0.15 beats. min(-1). mmHg(-1) in the control and heating periods, respectively). Neither the cool nor heat loadings altered the carotid baroreflex sensitivity in the HR control. These results suggest that the sensitivity of HR control by the extracarotid (presumably aortic) baroreflex was augmented by whole body skin cooling, whereas the sensitivities of HR control by arterial baroreflex remain unchanged during mild whole body heating in humans.     

Baroreflex control of muscle sympathetic nerve activity during skin surface cooling.

Skin surface cooling improves orthostatic tolerance through a yet to be identified mechanism. One possibility is that skin surface cooling increases the gain of baroreflex control of efferent responses contributing to the maintenance of blood pressure. To test this hypothesis, muscle sympathetic nerve activity (MSNA), arterial blood pressure, and heart rate were recorded in nine healthy subjects during both normothermic and skin surface cooling conditions, while baroreflex control of MSNA and heart rate were assessed during rapid pharmacologically induced changes in arterial blood pressure. Skin surface cooling decreased mean skin temperature (34.9 +/- 0.2 to 29.8 +/- 0.6 degrees C; P < 0.001) and increased mean arterial blood pressure (85 +/- 2 to 93 +/- 3 mmHg; P < 0.001) without changing MSNA (P = 0.47) or heart rate (P = 0.21). The slope of the relationship between MSNA and diastolic blood pressure during skin surface cooling (-3.54 +/- 0.29 units.beat(-1).mmHg(-1)) was not significantly different from normothermic conditions (-2.94 +/- 0.21 units.beat(-1).mmHg(-1); P = 0.19). The slope depicting baroreflex control of heart rate was also not altered by skin surface cooling. However, skin surface cooling shifted the "operating point" of both baroreflex curves to high arterial blood pressures (i.e., rightward shift). Resetting baroreflex curves to higher pressure might contribute to the elevations in orthostatic tolerance associated with skin surface cooling.     

Effects of a kappa-opioid agonist,asimadoline, on satiation and GI motor and sensory functions in humans

To compare the effects of the kappa-opioid agonist asimadoline and placebo on visceral sensation and gastrointestinal (GI) motor functions in humans, 91 healthy participants were randomized in a double-blind fashion to 0.15, 0.5, or 1.5 mg of asimadoline or placebo orally twice a day for 9 days. We assessed satiation (nutrient drink test), colonic compliance, tone, perception of colonic distension (barostat), and whole gut transit (scintigraphy). Treatment effect was assessed by analysis of covariance. Asimadoline increased nutrient drink intake (P = 0.03). Asimadoline decreased colonic tone during fasting (P = 0.03) without affecting postprandial colonic contraction, compliance, or transit. Gas scores in response to colonic distension were decreased with 0.5 mg of asimadoline at low levels (8 mmHg above operating pressure) of distension (P = 0.04) but not at higher levels of distension. Asimadoline at 1.5 mg increased gas scores at 16 mmHg of distension (P = 0.03) and pain scores at distensions of 8 and 16 mmHg (P = 0.003 and 0.03, respectively) but not at higher levels of distension. Further studies of this compound in diseases with altered satiation or visceral sensation are warranted.     

Effects of clothing pressure caused by different types of brassieres on autonomic nervous system activity evaluated by heart rate variability power spectral analysis

The present study was designed to investigate the effects of clothing skin pressures exerted by two different types of brassieres (a conventional higher skin-pressured brassiere and a newly devised low skin-pressured brassiere) on the autonomic nervous system (ANS) activity. Six healthy young women (22.8 +/- 1.4 yrs.) with regular menstrual cycles participated in this study. The ANS activities were assessed by means of heart rate variability power spectral analysis. The skin pressures exerted by the brassieres were measured with an air-pack type contact surface pressure sensor at five different points. The total amount of clothing pressure, and the pressures at the center and the side regions of the brassieres were significantly greater in the high than in the low skin-pressured brassiere (Total 9816.1 +/- 269.0 vs. 6436.8 +/- 252.4 Pa, P < 0.01; Center 2212.1 +/- 336.3 vs. 353.8 +/- 85.8 Pa, P < 0.01; Side 2556.8 +/- 316.1 vs. 1747.2 +/- 199.2 Pa, P < 0.05). Concerning the ANS activity, the Total power, and the very low frequency (VLF) and the high frequency (HF) components were significantly decreased in the high skin-pressured brassiere than those in the low skin-pressured brassiere (Total 531.6 +/- 57.3 vs. 770.5 +/- 54.2 ms2, P < 0.01; VLF 60.7 +/- 14.6 vs. 179.2 +/- 38.1 ms2, P < 0.05; HF 209.5 +/- 33.2 vs. 283.2 +/- 61.5 ms2, P < 0.01). Our data indicate that the higher clothing pressures exerted by a conventional brassiere have a significant negative impact on the ANS activity, which is predominantly attributable to the significant decrease in the parasympathetic as well as the thermoregulatory sympathetic nerve activities. Since the ANS activity plays an important role in modulating the internal environment in the human body, excess clothing pressures caused by constricting types of foundation garments on the body would consequently undermine women's health.     

Evidence of a myogenic response in vasomotor control of forearm and palm cutaneous microcirculations.

Previous investigations of autoregulatory mechanisms in the control of skin blood flow suffer from the possibility of interfering effects of the autonomic nervous system. To address this question, in 11 subjects cutaneous vascular responses were measured during acute changes in perfusion pressure (using Valsalva maneuver; VM) before and after ganglionic blockade via systemic trimethaphan infusion. Cutaneous vascular conductance at baseline (CVC(base)) and during the last 5 s of the VM (CVC(VM)) were measured from forearm (nonglabrous) and palm (glabrous) skin. During the VM without ganglionic blockade, compared with CVC(base), CVC(VM) decreased significantly at the palm [0.79 +/- 0.17 to 0.55 +/- 0.17 arbitrary units (AU)/mmHg; P = 0.002] but was unchanged at the forearm (0.13 +/- 0.02 to 0.16 +/- 0.02 AU/mmHg; P = 0.50). After ganglionic blockade, VM induced pronounced decreases in perfusion pressure, which resulted in significant increases in CVC(VM) at both forearm (0.19 +/- 0.03 to 0.31 +/- 0.07 AU/mmHg; P = 0.008) and palm (1.84 +/- 0.29 to 2.76 +/- 0.63 AU/mmHg; P = 0.003) sites. These results suggest that, devoid of autonomic control, both glabrous and nonglabrous skin are capable of exhibiting vasomotor autoregulation during pronounced reductions in perfusion pressure.     

Effect of doxazosin on insulin resistance in hypertensive patients with obesity.

We determined the effect of alpha-adrenergic blocking agent doxazosin on insulin resistance in 19 hypertensive patients (blood pressure [BP] >160/90 mmHg) with obesity (mean body mass index [BMI]: 26.7 +/- 1.9 kg/m (2)). Patients received doxazosin 4 mg/day for 12 months. Systolic and diastolic BP decreased from 169 +/- 10.8 mmHg to 147 +/- 11.9 mmHg (p < 0.0001) and from 102 +/- 8.1 mmHg to 87 +/- 5.0 mmHg (p < 0.0001), respectively. Insulin resistance and fasting immunoreactive insulin (IRI) were lower at study end vs. baseline (HOMA-R = 1.29 +/- 0.38 vs. 3.58 +/- 2.23 [p = 0.022]; IRI = 6.00 +/- 1.88 microU/ml vs 13.74 +/- 8.51 microU/ml [p = 0.046]). Total cholesterol was significantly reduced following treatment. Circulating TNF-alpha and leptin levels decreased significantly within 3 months of treatment; leptin was independently associated with insulin resistance when adjusted for BMI. We conclude that doxazosin improves insulin resistance and improves dyslipidemia in obese hypertensive patients, and has a beneficial effect on adipose endocrine activity.     

Epimerization of the four 3,7-dihydroxy bile acid epimers by human fecal microorganisms in anaerobic mixed cultures and in feces

The conversion of 3,7-dihydroxy bile acids by anaerobic mixed cultures of intestinal microorganisms was studied in fecal samples from eight healthy adult males. Incubations using substrate chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA) were performed simultaneously in separate microbial suspensions from the same fecal samples. A time course study was done on four samples, chosen randomly from the eight. In the incubation of CDCA, substrate CDCA always decreased rapidly in amount; UDCA increased in amount, as did 3 beta, 7 beta-dihydroxy-5 beta-cholanoic acid (3 beta, 7 beta) and 3 beta, 7 alpha-dihydroxy-5 beta-cholanoic acid (3 beta, 7 alpha). In the incubation of UDCA, UDCA gradually decreased in amount; (3 beta, 7 beta), CDCA, and (3 beta, 7 alpha) increased gradually in amount. All reactions involved four epimers. After 48-72 hr UDCA was predominant and the reactions appeared to have reached equilibrium. In cultures from all eight samples, after 72-96 hr, a predominance of beta-hydroxy configurations at 7-position and alpha-hydroxy configurations at 3-position was observed. To compare these bile acid compositions to those in feces, an in vivo study using nine subjects was carried out. Concurrent with the collection of feces, transit time of food through the gut was measured. In samples from five subjects, in which amounts of lithocholic acid (LCA) was small, four 3,7-dihydroxy epimers were found. In samples from the other four, however, CDCA, the predominant epimer in bile, had apparently been converted to LCA by 7-dehydroxylation, and four epimers were not always found. In contrast to the incubation study, UDCA was not always the predominant 3,7-dihydroxy epimer in the fecal study. This may have been due to the transit times, which averaged 26.4 +/- 8.9 SD hr, being much shorter than the time it took for the incubation reactions to reach equilibrium.     

Acute hypothyroidism slows the rate of left ventricular diastolic relaxation

The effect of acute thyroid hormone deficiency on left ventricular diastolic filling was studied by radionuclide ventriculography with simultaneous right heart catheterization in nine athyreotic patients without cardiovascular disease. The patients were studied when they were hypothyroid and when they were euthyroid on replacement therapy. Peak filling rate and the time to peak filling were used to characterize diastolic function. The time to peak filling was defined as the interval from end-systole on the radionuclide time-volume curve to the time of occurrence of peak filling. The peak filling rate was determined in absolute terms from the normalized radionuclide peak filling rate and from the end-diastolic volume, which was derived from the radionuclide ejection fraction and from the thermodilution stroke volume. In all patients, the values for peak filling rate were lower in the hypothyroid than in the euthyroid state (287 +/- 91 mL/s vs. 400 +/- 118 mL/s, delta = 41 +/- 13%, p less than 0.01). Peak filling always occurred during the first half of the diastolic interval. The time to peak filling was not significantly affected by the thyroid state (170 +/- 10 ms vs. 159 +/- 21 ms, delta = 7 +/- 10%). Left ventricular filling pressure as reflected by the pulmonary capillary wedge pressure and end-systolic volume were similar in both thyroid states (6 +/- 2 mmHg vs. 8 +/- 2 mmHg (1 mmHg = 133.32 Pa) and 32 +/- 11 mL vs. 32 +/- 7 mL, respectively). The data suggest that the rate of active diastolic relaxation is decreased in short-duration hypothyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Skin-surface cooling elicits peripheral and visceral vasoconstriction in humans.

Skin-surface cooling elicits a pronounced systemic pressor response, which has previously been reported to be associated with peripheral vasoconstriction and may not fully account for the decrease in systemic vascular conductance. To test the hypothesis that whole body skin-surface cooling would also induce renal and splanchnic vasoconstriction, 14 supine subjects performed 26 skin-surface cooling trials (15-18 degrees C water perfused through a tube-lined suit for 20 min). Oral and mean skin temperature, heart rate, stroke volume (Doppler ultrasound), mean arterial blood pressure (MAP), cutaneous blood velocity (laser-Doppler), and mean blood velocity of the brachial, celiac, renal, and superior mesenteric arteries (Doppler ultrasound) were measured during normothermia and skin-surface cooling. Cardiac output (heart rate x stroke volume) and indexes of vascular conductance (flux or blood velocity/MAP) were calculated. Skin-surface cooling increased MAP (n = 26; 78 +/- 5 to 88 +/- 5 mmHg; mean +/- SD) and decreased mean skin temperature (n = 26; 33.7 +/- 0.7 to 27.5 +/- 1.2 degrees C) and cutaneous (n = 12; 0.93 +/- 0.68 to 0.36 +/- 0.20 flux/mmHg), brachial (n = 10; 32 +/- 15 to 20 +/- 12), celiac (n = 8; 85 +/- 22 to 73 +/- 22 cm.s(-1).mmHg(-1)), superior mesenteric (n = 8; 55 +/- 16 to 48 +/- 10 cm.s(-1).mmHg(-1)), and renal (n = 8; 74 +/- 26 to 64 +/- 20 cm.s(-1).mmHg(-1); all P < 0.05) vascular conductance, without altering oral temperature, cardiac output, heart rate, or stroke volume. These data identify decreases in vascular conductance of skin and of brachial, celiac, superior mesenteric, and renal arteries. Thus it appears that vasoconstriction in both peripheral and visceral arteries contributes importantly to the pressor response produced during skin-surface cooling in humans.     

Carotid baroreflex responsiveness in heat-stressed humans

The effects of whole body heating on human baroreflex function are relatively unknown. The purpose of this project was to identify whether whole body heating reduces the maximal slope of the carotid baroreflex. In 12 subjects, carotid-vasomotor and carotid-cardiac baroreflex responsiveness were assessed in normothermia and during whole body heating. Whole body heating increased sublingual temperature (from 36.4 +/- 0.1 to 37.4 +/- 0.1 degrees C, P < 0.01) and increased heart rate (from 59 +/- 3 to 83 +/- 3 beats/min, P < 0. 01), whereas mean arterial blood pressure (MAP) was slightly decreased (from 88 +/- 2 to 83 +/- 2 mmHg, P < 0.01). Carotid-vasomotor and carotid-cardiac responsiveness were assessed by identifying the maximal gain of MAP and heart rate to R wave-triggered changes in carotid sinus transmural pressure. Whole body heating significantly decreased the responsiveness of the carotid-vasomotor baroreflex (from -0.20 +/- 0.02 to -0.13 +/- 0.02 mmHg/mmHg, P < 0.01) without altering the responsiveness of the carotid-cardiac baroreflex (from -0.40 +/- 0.05 to -0.36 +/- 0.02 beats x min(-1) x mmHg(-1), P = 0.21). Carotid-vasomotor and carotid-cardiac baroreflex curves were shifted downward and upward, respectively, to accommodate the decrease in blood pressure and increase in heart rate that accompanied the heat stress. Moreover, the operating point of the carotid-cardiac baroreflex was shifted closer to threshold (P = 0.02) by the heat stress. Reduced carotid-vasomotor baroreflex responsiveness, coupled with a reduction in the functional reserve for the carotid baroreflex to increase heart rate during a hypotensive challenge, may contribute to increased susceptibility to orthostatic intolerance during a heat stress.     

In vivo studies of sterol and squalene secretion by human skin

This work was aimed at studying the quantity and composition of sterols and squalene secreted by the human skin. Lipids secreted by the entire skin were recovered by Soxhlet extraction of the clothing worn by a patient for 24 hr with a chloroform-methanol azeotrope and by extracting the water of a shower taken by the patient at the end of the 24-hr period. Squalene and sterols were quantified by gas-liquid chromatography. Plant sterols were separated from total sterols by thin-layer chromatography. Free and esterified cholesterol were separated by digitonin precipitation. In eight adults, seven of them with hyperlipoproteinemia, the total skin secretion of cholesterol ranged from 59 to 108 mg/day, with a mean of 88 +/- 17 (SD) mg/day. There was no difference in cholesterol secretion between the normocholesterolemic individual and the hypercholesterolemic ones, nor were there any differences according to type of hyperlipoproteinemia. Free cholesterol amounted to 54 +/- 5% of the total cholesterol. The secretion of squalene ranged from 125 to 475 mg/day in five patients. The secretion of both squalene and cholesterol was quite constant for any individual on a given diet. Cholesterol constituted 95.6 +/- 0.5% of the digitonin-precipitable total body surface sterols of eight patients, and lathosterol, the next largest fraction, 3.4 +/- 0.4%. Total plant sterols formed only 0.65 +/- 0.38% and beta-sitosterol 0.35 +/- 0.23% of the skin surface sterols in six patients whose dietary beta-sitosterol intake ranged from 230 to 3400 mg/day.     

Transmural pressure in rat initial subpleural lymphatics during spontaneous or mechanical ventilation

The role played by the mechanical tissue stress in supporting lymph formation and propulsion in thoracic tissues was studied in deeply anesthetized rats (n = 13) during spontaneous breathing or mechanical ventilation. After arterial and venous catheterization and insertion of an intratracheal cannula, fluorescent dextrans were injected intrapleurally to serve as lymphatic markers. After 2 h, the fluorescent intercostal lymphatics were identified, and the hydraulic pressure in lymphatic vessels (P lymph) and adjacent interstitial space (P int) was measured using micropuncture. During spontaneous breathing, end-expiratory P lymph and corresponding P int were -2.5 +/- 1.1 (SE) and 3.1 +/- 0.7 mmHg (P < 0.01), which dropped to -21.1 +/- 1.3 and -12.2 +/- 1.3 mmHg, respectively, at end inspiration. During mechanical ventilation with air at zero end-expiratory alveolar pressure, P lymph and P int were essentially unchanged at end expiration, but, at variance with spontaneous breathing, they increased at end inspiration to 28.1 +/- 7.9 and 28.2 +/- 6.3 mmHg, respectively. The hydraulic transmural pressure gradient (DeltaP tm = P lymph - P int) was in favor of lymph formation throughout the whole respiratory cycle (DeltaP tm = -6.8 +/- 1.2 mmHg) during spontaneous breathing but not during mechanical ventilation (DeltaP tm = -1.1 +/- 1.8 mmHg). Therefore, data suggest that local tissue stress associated with the active contraction of respiratory muscles is required to support an efficient lymphatic drainage from the thoracic tissues.