RESUMEN
We used ultrasound to study venous return during heat stress. We measured venous cross-sectional area (CSA) and blood flow velocity (BFV) of nine femoral veins and nine saphenous veins. During heat stress, saphenous CSA increased from 4.7 +/- 2.6 mm2 (mean +/- SD) to 9.1 +/- 2.3 mm2 (P < 0.01), whereas femoral CSA was 22.7 +/- 9.5 mm2 at rest and 22.0 +/- 9.6 mm2 during heat stress (NS). Meanwhile, BFV increased from 0.06 +/- 0.02 to 0.30 +/- 0.10 m/s (P < 0.01) in the saphenous vein and from 0.14 +/- 0.08 to 0.38 +/- 0.23 m/s (P < 0.005) in the femoral vein. Maximal venous outflow (MVO) was the product of CSA and BFV. During heat stress, MVO showed an eightfold increase in the saphenous veins (from 22.7 +/- 18.2 to 180.7 +/- 86.7 ml/min) and a 2.5-fold increase in the femoral veins (from 143.4 +/- 52.9 to 354.0 +/- 126.9 ml/min). The results showed that one-half of the cutaneous blood flow increase during heat stress returned through the deep collecting veins in the lower limb. Thereafter, although there was no venodilation of deep veins compared with superficial veins, the deep veins remain the main pathway for the venous return during heat stress.
Asunto(s)
Vena Femoral/fisiología , Hemodinámica , Calor , Pierna/irrigación sanguínea , Músculos/irrigación sanguínea , Vena Safena/fisiología , Adulto , Velocidad del Flujo Sanguíneo , Presión Sanguínea , Femenino , Vena Femoral/diagnóstico por imagen , Vena Femoral/fisiopatología , Frecuencia Cardíaca , Humanos , Flujometría por Láser-Doppler , Masculino , Músculos/diagnóstico por imagen , Flujo Sanguíneo Regional , Vena Safena/diagnóstico por imagen , Vena Safena/fisiopatología , Estrés Fisiológico/fisiopatología , Factores de Tiempo , UltrasonografíaRESUMEN
Unlike most studies on deep veins performed with simultaneous suppression of cutaneous blood flow, a sonographic study of femoral diameter and blood flow velocity changes in response to thermal stress was performed while cutaneous flow was preserved. In 11 normal subjects, mean peak blood flow velocity and diameter of the femoral vein were measured at rest and during indirect whole body heating and cooling. Mean peak venous blood flow velocity was 0.12 +/- 0.06 m s-1 at rest, 0.35 +/- 0.23 m s-1 (P < 0.001) during heat stress, and 0.13 +/- 0.07 m s-1 during cold stress (NS). Femoral venous diameter was 5.3 +/- 0.9 mm at rest, 5.1 +/- 1.0 mm (P < 0.05) during warming, and 5.4 +/- 81.0 mm (NS) during cooling. This study showed a decrease in diameter during thermal stress. However, as mean femoral venous blood-flow velocity was doubled during heat stress, femoral venous blood flow was increased. Thus, it is suggested that during heat stress part of the increase in cutaneous flow is returned through deep veins.
Asunto(s)
Vena Femoral/fisiopatología , Calor/efectos adversos , Estrés Fisiológico/fisiopatología , Vasodilatación/fisiología , Adulto , Presión Sanguínea/fisiología , Vena Femoral/diagnóstico por imagen , Frecuencia Cardíaca/fisiología , Humanos , Masculino , Flujo Sanguíneo Regional/fisiología , Temperatura Cutánea/fisiología , Estrés Fisiológico/diagnóstico por imagen , UltrasonografíaRESUMEN
Although volume, pressure or flow in superficial veins have been studied extensively, little is known about venous blood velocity during thermal stress. Most authors have suggested that the velocity is decreased in the dilated superficial veins during heat stress to facilitate heat loss, and is increased during cooling as the vein is constricted. Duplex ultrasound has been used to study saphenous cross sectional area (CSA) and mean maximal venous blood velocity (BV) in ten healthy volunteers (age 22-31 years). Compared with unstressed mean values, 4.8 (SD 2.6) mm2, CSA increased to 9.3 (SD 2.1) mm2 (P < 0.005) during heat stress and decreased to 2.1 (SD 1.9) mm2 (P < 0.005) during cold stress. These results are consistent with previous studies, but the absolute CSA of the saphenous vein has never been estimated during thermal stress. The BV increased from 0.07 (SD 0.02) m.s-1 to 0.29 (SD 0.11) m.s-1 (P < 0.005) during warming. During cooling, BV tended to decrease: 0.05 (SD 0.03) m.s-1 (N.S). We would suggest that heat loss during thermal stress can be facilitated by the rapid turnover of warm blood, and not (as usually suggested) by the prolonged cooling of each blood sample in the dilated superficial veins.
Asunto(s)
Velocidad del Flujo Sanguíneo/fisiología , Frío/efectos adversos , Calor/efectos adversos , Vena Safena/fisiología , Estrés Fisiológico/fisiopatología , Adulto , Presión Sanguínea , Femenino , Frecuencia Cardíaca , Humanos , Masculino , Vena Safena/diagnóstico por imagen , Ultrasonografía , Presión VenosaRESUMEN
In the present study, heat thermal clearance (HTC) was compared to laser Doppler flowmetry (LDF) and transcutaneous oxygen pressure (tcPO2), measured on the forefoot of 17 patients with vascular intermittent claudication and 10 controls in various positions at rest and after a treadmill exercise test. The mean ankle brachial systolic pressure ratio (ABSP) of the patients, measured using ultrasonic Doppler velocimetry, was 0.53 +/- 0.05. Their walking distance was 480 +/- 100 meters, the treadmill exercise being stopped as soon as pain sensation. No statistically significant difference was found between patients and controls for HTC, LDF, tc P02, forefoot and ankle skin temperatures. Statistically significant differences between patients and controls occurred in the sitting position for tcPO2, in standing position for HTC and after treadmill exercise for tcPO2 and LDF. When assuming the sitting position HTC did not vary significantly in patients and decreased in controls, LDF decreased and tcPO2 increased in both groups. After treadmill exercise, HTC in patients did not vary compared to supine values and HTC decreased in controls, tcPO2 remained unchanged in controls and decreased in patients, LDF increased in controls and decreased in patients. No significant correlations were found between the different techniques measured at rest in patients and controls. However in patients, after the treadmill test, LDF correlated with the walking distance (r = 0.667) and with ABSP (r = 0.641), HTC inversely correlated with the walking distance (r = -0.680) and ABSP (r = -0.577). Laser Doppler, tcPO2 and HTC are useful as tools to understand the alterations of cutaneous microcirculation of the lower limbs in patients with V.I.C.. However their results need to be interpreted with caution because these methods do not measure directly blood flow.
Asunto(s)
Monitoreo de Gas Sanguíneo Transcutáneo , Claudicación Intermitente/fisiopatología , Flujometría por Láser-Doppler , Temperatura Cutánea , Piel/irrigación sanguínea , Adulto , Anciano , Presión Sanguínea , Prueba de Esfuerzo , Pie/irrigación sanguínea , Humanos , Masculino , Microcirculación , Persona de Mediana Edad , Flujo Sanguíneo Regional , Piel/diagnóstico por imagen , Conductividad Térmica , Ultrasonografía , VasodilataciónRESUMEN
To determine the role of the active cutaneous vasodilatator response in forearm and finger skin, direct assessment of only skin blood flow was performed before and after musculocutaneous and median nerve blockade during whole body heating and cooling. Forearm laser Doppler flow (LDF forearm), forearm heat thermal clearance (HTC forearm), and finger laser Doppler flow (LDF finger) were monitored in the nerve blocked skin and contralateral untreated skin (control). In the pre-blockade period, no significant differences were found between experimental and control arm skin. After nerve block a significant increase occurred only in LDF finger, which rose from 4.3 +/- 0.6 to 6.0 +/- 0.5 volts (p less than 0.05). During whole body heating LDF forearm and HTC forearm increased significantly on both arms. The increase in LDF forearm was greater (p less than 0.05) in control (18.3 +/- 1.2 volts) than in nerve blocked skin (14.6 +/- 1.8 volts) and occurred earlier. The same tendency was observed in HTC forearm between nerve blocked skin (0.522 +/- 0.06 W.m-1.degrees C-1) and control 0.671 +/- 0.037 W.m-1.degrees C-1) (NS). LDF raise up to 6.6 +/- 0.5 and 6.8 +/- 0.5 volts in the blocked finger and in the control respectively. During cooling LDF finger in the control decreased to 1.3 +/- 0.1 volt and was significantly (p less than 0.05) lower than in the resting period, and lower than that in the nerve blocked finger (3.4 +/- 0.8 volts) (p less than 0.05). We conclude that the active vasodilatator system plays an important role as far as the timing and the amplitude of the cutaneous vasodilatator response to whole body heating in the forearm but not in the finger. At thermal neutrality, the vascular vasoconstrictor tone is high to the finger but not to the forearm. The vasoconstrictor response to cooling occurred only in the finger.
Asunto(s)
Bloqueo Nervioso Autónomo , Regulación de la Temperatura Corporal/fisiología , Frío , Dedos/irrigación sanguínea , Antebrazo/irrigación sanguínea , Calor , Piel/irrigación sanguínea , Sistema Vasomotor/fisiología , Adulto , Femenino , Dedos/inervación , Antebrazo/inervación , Hemodinámica , Humanos , Masculino , Nervio Mediano/fisiología , Microcirculación , Flujo Sanguíneo Regional , Piel/inervaciónRESUMEN
The automation of equipment is essential in laboratories performing a large number of procedures with high precision. An evaluation of performance characteristics of a photoelectric automated coagulation instrument, the Coagulyzer II (Lancer) is reported and compared with performances of the Coag-a-pet 200.