Hypothermia and rewarming after hypothermic exposure alter venous relaxation

Effects of heat waves and cold spells on blood parameters: a cohort study of blood donors in Tianjin, China

BACKGROUND

With the increasing occurrence of extreme temperature events due to climate change, the attention has been predominantly focused on the effects of heat waves and cold spells on morbidity and mortality. However, the influence of these temperature extremes on blood parameters has been overlooked.

METHODS

We conducted a cohort study involving 2,752 adult blood donors in Tianjin, China, between January 18, 2013, and June 25, 2021. The generalized additive mixed model was used to investigate the effects and lagged effects of heat waves and cold spells on six blood parameters of blood donors, including alanine aminotransferase (ALT), white blood cell count (WBC), red blood cell count (RBC), hemoglobin (HB), hematocrit (HCT), and platelet count (PLT). Subgroup analyses were stratified by sex, age, and BMI.

RESULTS

Heat waves and cold spells are associated with changes in blood parameters, particularly HB and PLT. Heat waves increased HB and PLT, while cold spells increased HB and decreased PLT. The effect of heat waves is greater than that of cold spells. The largest effect of heat waves on HB and PLT occurred at lag1 with 2.6 g/L (95% CI: 1.76 to 3.45) and lag7 with 9.71 × 10^9/L (95% CI: 6.26 to 13.17), respectively, while the largest effect of cold spells on HB and PLT occurred at lag0 with 1.02 g/L (95% CI: 0.71 to 1.33) and lag2 with -3.85 × 10^9/L (95% CI: -5.00 to -2.70), respectively. In subgroup analysis, the effect of cold spells on ALT was greater in the 40-49 age group.

CONCLUSION

We indicated that heat waves and cold spells can impact hemoglobin and platelet counts in the human body. These findings provide evidence linking heat waves or cold spells to diseases and may reduce health risks caused by extreme temperature events.

Vasoreactivity of the Murine External Jugular Vein and Carotid Artery

INTRODUCTION

Impaired venous reactivity has potential to contribute to clinically significant pathologies such as arteriovenous fistula (AVF) maturation failure. Vascular segments commonly used in murine preclinical models of AVF include the carotid artery and external jugular vein. Detailed descriptions of isometric procedures to evaluate function of murine external jugular vein ex vivo have not been previously published.

OBJECTIVE

To establish isometric procedures to measure naive murine external jugular vein reactivity ex vivo.

METHODS

Vasomotor responses of external jugular veins and ipsilateral common carotid arteries from C57BL/6 mice were evaluated using isometric tension procedures.

RESULTS

External jugular veins developed tension (p < 0.05) to potassium chloride and U-46619, but not to phenylephrine, whereas common carotid arteries responded to all 3 agents (p < 0.05). While maximal responses to acetylcholine (ACh) were similar between the venous and arterial segments, the dose required to achieve this value was lower (p < 0.05) in the artery versus vein. Nitric oxide synthase inhibition attenuated (p < 0.05) but did not abolish ACh-evoked vasorelaxation in both vascular segments, whereas cyclooxygenase blockade had no effect. Endothelium-independent vasorelaxation to sodium nitroprusside was similar in the artery and vein.

CONCLUSION

Vasorelaxation and vasocontraction can be reliably assessed in the external jugular vein in C57BL/6 mice using isometric procedures.

Cardiac condition during cooling and rewarming periods of therapeutic hypothermia after cardiopulmonary resuscitation

BACKGROUND

Hypothermia has been used in cardiac surgery for many years for neuroprotection. Mild hypothermia (MH) [body temperature (BT) kept at 32-35°C] has been shown to reduce both mortality and poor neurological outcome in patients after cardiopulmonary resuscitation (CPR). This study investigated whether patients who were expected to benefit neurologically from therapeutic hypothermia (TH) also had improved cardiac function.

METHODS

The study included 30 patients who developed in-hospital cardiac arrest between September 17, 2012, and September 20, 2013, and had return of spontaneous circulation (ROSC) following successful CPR. Patient BTs were cooled to 33°C using intravascular heat change. Basal BT, systolic artery pressure (SAP), diastolic artery pressure (DAP), mean arterial pressure (MAP), heart rate, central venous pressure, cardiac output (CO), cardiac index (CI), global end-diastolic volume index (GEDI), extravascular lung water index (ELWI), and systemic vascular resistance index (SVRI) were measured at 36°C, 35°C, 34°C and 33°C during cooling. BT was held at 33°C for 24 hours prior to rewarming. Rewarming was conducted 0.25°C/h. During rewarming, measurements were repeated at 33°C, 34°C, 35°C and 36°C. A final measurement was performed once patients spontaneously returned to basal BT. We compared cooling and rewarming cardiac measurements at the same BTs.

RESULTS

SAP values during rewarming (34°C, 35°C and 36°C) were lower than during cooling (P < 0.05). DAP values during rewarming (basal temperature, 34°C, 35°C and 36°C) were lower than during cooling. MAP values during rewarming (34°C, 35°C and 36°C) were lower than during cooling (P < 0.05). CO and CI values were higher during rewarming than during cooling. GEDI and ELWI did not differ during cooling and rewarming. SVRI values during rewarming (34°C, 35°C, 36°C and basal temperature) were lower than during cooling (P < 0.05).

CONCLUSIONS

To our knowledge, this is the first study comparing cardiac function at the same BTs during cooling and rewarming. In patients experiencing ROSC following CPR, TH may improve cardiac function and promote favorable neurological outcomes.