Continuous monitoring of haemodynamic parameters in humans during the early phase of simulated diving with and without breathholding

A Comprehensive Review of Magnesium Sulfate Infusion: Unveiling the Impact on Hemodynamic Stability During Laryngoscopy and Tracheal Intubation in Ear, Nose, and Throat Surgeries

This comprehensive review explores the potential of magnesium sulfate infusion in mitigating hemodynamic instability during laryngoscopy and tracheal intubation in ear, nose, and throat (ENT) surgeries. Hemodynamic fluctuations during these procedures pose challenges, and magnesium sulfate, with its vasodilatory, antiarrhythmic, and neuroprotective properties, emerges as a promising intervention. The review critically examines existing literature, emphasizing patient selection criteria, dosage protocols, and a comparative analysis with other hemodynamic stabilizers. Safety considerations, including known adverse effects and risk-benefit assessments, and monitoring and management strategies are elucidated. The implications for ENT surgery are discussed, highlighting the potential for enhanced hemodynamic management and individualized approaches. The review concludes with a call for continued research, emphasizing the ongoing evolution of understanding and practice incorporating magnesium sulfate into perioperative care. The insights offered aim to guide clinicians in navigating this dynamic landscape for improved patient outcomes in ENT surgeries.

Cold Pressor Stress Cardiac Magnetic Resonance Myocardial Flow Reserve Is Not Useful for Detection of Coronary Endothelial Dysfunction in Women with Signs and Symptoms of Ischemia and No Obstructive CAD

BACKGROUND

Coronary endothelial function testing using acetylcholine is not routinely available, while non-pharmacological cold pressor testing (CPT) is considered an endothelial stressor. Noninvasive cardiac magnetic resonance imaging (CMRI) myocardial perfusion reserve index (MPRI) can detect coronary microvascular dysfunction (CMD). We evaluated if CPT stress CMRI MPRI could detect invasive coronary endothelial dysfunction.

METHODS

Coronary reactivity testing was performed in 189 women with symptoms and signs of ischemic but no obstructive coronary artery disease as previously described plus CPT stress. Subjects also underwent pharmacologic and CPT stress during CMRI (1.5 T). Statistical analysis comparing CPT MPRI between groups was performed by Welch`s t-test and Mann-Whitney where appropriate. Anderson-Darling test and Levene test were considered to verify the normality and homogeneity of variances assumptions. Correlation analyses between CPT MPRI and both invasive and noninvasive measures of CMD were performed using Spearman correlation.

RESULTS

While CPT MPRI correlated with pharmacological stress MPRI, it did not correlate with invasive measures of CMD including invasively measured responses to intracoronary (IC) adenosine, IC acetylcholine, CPT, or IC nitroglycerin. Additionally CPT MPRI was not significantly different between subjects with normal compared to abnormal pharm stress MPRI or normal compared to abnormal invasive CMD parameters.

CONCLUSION

Despite correlation with pharmacological stress MPRI, non-invasive CPT MPRI does not appear to be useful for detecting CMD in symptomatic women.

Diving into the Ice Bucket Challenge: Intraparenchymal Hemorrhage and the Mammalian Diving Reflex

Triggered by facial exposure to cold water and apnea, the mammalian diving reflex consists of bradycardia and peripheral arteriolar vasoconstriction leading to an increase in central arterial pressure. It has been previously associated with ischemic stroke but not definitively with intracerebral hemorrhage. We present a case of intracerebral hemorrhage occurring in a woman with poorly controlled hypertension following her participation in the amyotrophic lateral sclerosis fund-raising "Ice Bucket Challenge," in which ice-cold water was poured on her head. We suspect that facial exposure to ice-cold water triggered the diving reflex, causing a hypertensive surge and ultimately the intracerebral hemorrhage.

The trigeminocardiac reflex - a comparison with the diving reflex in humans

The trigeminocardiac reflex (TCR) has previously been described in the literature as a reflexive response of bradycardia, hypotension, and gastric hypermotility seen upon mechanical stimulation in the distribution of the trigeminal nerve. The diving reflex (DR) in humans is characterized by breath-holding, slowing of the heart rate, reduction of limb blood flow and a gradual rise in the mean arterial blood pressure. Although the two reflexes share many similarities, their relationship and especially their functional purpose in humans have yet to be fully elucidated. In the present review, we have tried to integrate and elaborate these two phenomena into a unified physiological concept. Assuming that the TCR and the DR are closely linked functionally and phylogenetically, we have also highlighted the significance of these reflexes in humans.

Cardiac changes induced by immersion and breath-hold diving in humans

To evaluate the separate cardiovascular response to body immersion and increased environmental pressure during diving, 12 healthy male subjects (mean age 35.2 ± 6.5 yr) underwent two-dimensional Doppler echocardiography in five different conditions: out of water (basal); head-out immersion while breathing ( condition A); fully immersed at the surface while breathing ( condition B) and breath holding ( condition C); and breath-hold diving at 5-m depth ( condition D). Heart rate, left ventricular volumes, stroke volume, and cardiac output were obtained by underwater echocardiography. Early (E) and late (A) transmitral flow velocities, their ratio (E/A), and deceleration time of E (DTE) were also obtained from pulsed-wave Doppler, as left ventricular diastolic function indexes. The experimental protocol induced significant reductions in left ventricular volumes, left ventricular stroke volume ( P < 0.05), cardiac output ( P < 0.001), and heart rate ( P < 0.05). A significant increase in E peak ( P < 0.01) and E/A ( P < 0.01) and a significant reduction of DTE ( P < 0.01) were also observed. Changes occurring during diving ( condition D) accounted for most of the changes observed in the experimental series. In particular, cardiac output at condition D was significantly lower compared with each of the other experimental conditions, E/A was significantly higher during condition D than in conditions A and C. Finally, DTE was significantly shorter at condition D than in basal and condition C. This study confirms a reduction of cardiac output in diving humans. Since most of the changes were observed during diving, the increased environmental pressure seems responsible for this hemodynamic rearrangement. Left ventricular diastolic function changes suggest a constrictive effect on the heart, possibly accounting for cardiac output reduction.

Simulated human diving and heart rate: making the most of the diving response as a laboratory exercise

Laboratory exercises in which students examine the human diving response are widely used in high school and college biology courses despite the experience of some instructors that the response is unreliably produced in the classroom. Our experience with this exercise demonstrates that the bradycardia associated with the diving response is a robust effect that can easily be measured by students without any sophisticated measurement technology. We discuss measures that maximize the success of the exercise by reducing individual variation, designing experiments that are minimally affected by change in the response over time, collecting data in appropriate time increments, and applying the most powerful statistical analysis. Emphasis is placed on pedagogical opportunities for using this exercise to teach general principles of physiology, experimental design, and data analysis. Data collected by students, background information for instructors, a discussion of the relevance of the diving reflex to humans, suggestions for additional experiments, and thought questions with sample answers are included.