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J Hynson

Publications and source records attributed to J Hynson.

8 recordsLinked to original sources
PubMed1999

A new noninvasive method to measure blood pressure: results of a multicenter trial.

BACKGROUND: Blood pressure (BP) monitoring with arterial waveform display requires an arterial cannula. We evaluated a new noninvasive device, Vasotrac (Medwave, Arden Hills, MN) that provides BP measurements approximately every 12-15 beats and displays pulse rate and a calibrated arterial waveform for each BP measurement. METHODS: Surgical and critically ill patients (n = 80) served as subjects for the study. BPs, pulse waveforms, and pulse rates measured via a radial artery catheter were compared with those obtained by the Vasotrac from the opposite radial artery. Data were analyzed to determine agreement between the two systems of measurement. RESULTS: Blood pressure measured noninvasively by the Vasotrac demonstrated excellent correlation (P<0.01) with BP measured via a radial arterial catheter (systolic r2 = 0.93; diastolic r2 = 0.89; mean r2 = 0.95). Differences in BP measured by the Vasotrac versus the radial arterial catheter were small. The mean+/-SD bias and precision were as follows: systolic BP 0.02+/-5.4 mm Hg and 3.9+/-3.7 mm Hg; diastolic BP -0.39+/-3.9 mm Hg and 2.7+/-2.8 mm Hg; mean BP -0.21+/-3.0 mm Hg and 2.1+/-2.2 mm Hg compared with radial artery measurements. The Vasotrac pulse rates were almost identical to those measured directly (r2 = 0.95). The Vasotrac BP waveform resembled those directly obtained radial artery pulsatile waveforms. CONCLUSIONS: In surgical and critically ill patients, the Vasotrac measured BP, pulse rate, and displayed radial artery waveform, which was similar to direct radial arterial measurements. It should be a suitable device to measure BP frequently in a noninvasive fashion.

Adult↗
PubMed1993

Preanesthetic skin-surface warming reduces redistribution hypothermia caused by epidural block.

Redistribution of heat from the core to the cool peripheral compartments of the body causes hypothermia during epidural anesthesia. Diminishing the temperature gradient between the core and peripheral tissues by warming the body via the skin before anesthesia should prevent this hypothermia. We measured core temperature, skin temperatures, and cutaneous heat loss in seven volunteers who received two lidocaine epidural injections during a single study day. One epidural injection was given after the volunteer had rested in a cool room (approximately 22 degrees C) ("no prewarming") for 2 h, and one injection was given after the volunteer had been covered with a forced air warming mattress (approximately 38 degrees C) ("prewarming") for 2 h. Skin temperatures were higher after prewarming. The decrease in core temperature during epidural anesthesia was smaller after prewarming [mean within patient difference (prewarming-no prewarming): 0.41; P = 0.003]. However, heat loss was greater after prewarming (mean within patient difference: 26.4; P = 0.02). Shivering was less after prewarming. We conclude that prewarming decreases redistribution hypothermia caused by epidural block. These results support the hypothesis that redistribution of heat within the body, not heat loss, is the most important etiology of hypothermia from epidural anesthesia.

Adult↗
PubMed1992

Thermoregulatory vasoconstriction during isoflurane anesthesia minimally decreases cutaneous heat loss.

The authors tested the extent to which thermoregulatory vasoconstriction decreases cutaneous heat loss during isoflurane anesthesia. Thermoregulatory vasoconstriction was provoked by central hypothermia in five nonsurgical volunteers given isoflurane anesthesia. Peripheral arteriovenous shunt flow was quantified using forearm-fingertip skin-surface temperature gradients and volume plethysmography. Capillary blood flow on the chest was evaluated using laser Doppler flowmetry. The central temperature triggering peripheral vasoconstriction (the thermoregulatory threshold) was 34.6 +/- 0.4 degrees C. Central body temperature decreased less than or equal to 0.2 degrees C in the period from 1 h preceding onset of significant vasoconstriction until 1.5 h afterward. Chest skin-surface blood flow decreased 21% during the period from 2 h before to 1 h after significant fingertip vasoconstriction. In contrast, fingertip blood flow decreased approximately 50-fold in the same period. The correlation between fingertip blood flow and skin-temperature gradient was excellent. Total heat loss decreased approximately 26% (25.3 +/- 3.9 W) in the period from 2 h before significant peripheral vasoconstriction to 1 h afterward. Loss from the arms and legs (upper arm, lower arm, thigh, and calf) decreased approximately 24% in the same period. Heat loss from the trunk and head decreased only 14%; in contrast, loss from the hands and feet decreased approximately 57%. There were no clinically important changes in blood pressure or heart rate during vasoconstriction, but oxyhemoglobin saturation (measured by pulse oximetry) increased slightly. These data suggest that thermoregulatory vasoconstriction only minimally decreases cutaneous heat loss.

Adult↗
PubMed1992

Painful stimulation minimally increases the thermoregulatory threshold for vasoconstriction during enflurane anesthesia in humans.

Generalized autonomic stimulation enhances hemodynamic responses and may, in a similar fashion, facilitate thermoregulatory responses. We thus tested the hypothesis that painful stimulation increases the central temperature threshold for vasoconstriction during general anesthesia. Healthy volunteers were anesthetized with 1.3% end-tidal enflurane on 2 separate days. On 1 day (randomly assigned), painful stimulation was produced by tetanic electrical stimulation. On the other day, electrical stimulation was not given. Significant thermoregulatory vasoconstriction was defined as a forearm-fingertip skin-surface temperature gradient exceeding 4 degrees C. The distal esophageal temperature triggering significant vasoconstriction was considered the thermoregulatory threshold. The threshold was 35.5 +/- 0.8 degrees C during electrical stimulation and 35.1 +/- 0.6 degrees C without stimulation (P = 0.050, 95% confidence interval for the difference = 0-0.7 degree C). These data suggest that thresholds determined in nonsurgical volunteers will be slightly (but not clinically significantly) less than those in operative patients. Similarly, intraoperative vasoconstriction thresholds likely will be slightly less when surgical pain is prevented by simultaneous regional or local analgesia.

Adult↗
PubMed1991

Isoflurane-induced vasodilation minimally increases cutaneous heat loss.

Central body temperature, which usually is well controlled, typically decreases more than 1 degree C during the 1st h of general anesthesia. This hypothermia has been attributed partially to an anesthetic-induced peripheral vasodilation, which increases cutaneous heat loss to the environment. Based on the specific heat of humans, heat loss would have to increase more than 70 W for 1 h (in a 70-kg person) to explain hypothermia after induction of general anesthesia. However, during epidural anesthesia, sympathetic blockade increases heat loss only slightly. Furthermore, thermoregulatory vasoconstriction in unanesthetized humans decreases heat loss to the environment only 15 W. Therefore, we tested the hypothesis that the hypothermia that follows induction of general anesthesia does not result from increased cutaneous heat loss. Heat loss and skin-surface and tympanic membrane temperatures, before and after induction of isoflurane anesthesia, were measured in five minimally clothed volunteers. Peripheral skin blood flow was evaluated with venous-occlusion volume plethysmography and skin-surface temperature gradients. Cutaneous heat losses in watts were summed from ten area-weighted thermal flux transducers. Tympanic membrane temperature, which was stable during the 30-min control period preceding induction, decreased 1.2 +/- 0.2 degrees C in the 50 min after induction. Isoflurane anesthesia decreased mean arterial blood pressure approximately 20%. Average skin-surface temperature increased over 15 min to 0.5 degree C above control. Heat loss from the trunk, head, arms, and legs decreased slightly, whereas loss from the hands and feet (10.5% of the body surface area) doubled (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Thermoregulatory vasoconstriction decreases cutaneous heat loss.

To determine the extent to which thermoregulatory vasoconstriction decreases heat loss to the environment, we measured regional heat flux, average skin temperature, and tympanic membrane temperature before and after thermoregulatory vasoconstriction in five minimally clothed volunteers maintained in a 30.8 +/- 0.1 degrees C environment. Thermoregulatory vasoconstriction was induced by central venous infusion of cooled fluid. Peripheral cutaneous blood flow was evaluated with venous-occlusion volume plethysmography and skin-surface temperature gradients. Laser Doppler flowmetry was used to measure vasoconstriction in centrally located skin. This model mimics the common clinical situation in which patients in a warm environment are centrally cooled by administration of cold intravenous fluids or by lavage of internal cavities with cold fluids. Tympanic membrane temperature decreased 1.5 +/- 0.3 degrees C in the first 15 min after the cold fluid infusion was started and remained approximately 1 degrees C below control values during the rest of the study. Average skin-surface temperature decreased slowly to approximately 0.7 degrees C below control. Flow in capillaries of centrally distributed skin, determined with laser Doppler flowmetry, decreased only approximately 40%. Total heat flux, and flux from the arms and legs decreased approximately 25% (15.5 +/- 0.3 W). Heat loss from the trunk and head decreased only 17%, whereas, loss from the hands and feet (10.5% of the body surface area) decreased approximately 50%. All measured values decreased significantly following vasoconstriction (P less than 0.01). Therefore, thermoregulatory vasoconstriction in a thermoneutral environment appears to decrease cutaneous loss of metabolic heat approximately 25%.

Adult↗