Influence of increased plasma osmolality on sympathetic outflow during apnea.

Animal models have shown that peripheral chemoreceptors alter their firing patterns in response to changes in plasma osmolality, which, in turn, may modulate sympathetic outflow. The purpose of this study was to test the hypothesis that increases in plasma osmolality augment muscle sympathetic nerve activity (MSNA) responses to chemoreceptor activation. MSNA was recorded from the peroneal nerve (microneurography) during a 23-min intravenous hypertonic saline infusion (3% NaCl; HSI). Chemoreceptor activation was elicited by voluntary end-expiratory apnea. MSNA responses to end-expiratory apnea were calculated as the absolute increase from the preceding baseline period. Plasma osmolality significantly increased from pre- to post-HSI (284 ± 1 to 290 ± 1 mOsm/kg H(2)O; P < 0.01). There was a significant overall effect of osmolality on sympathetic activity (P < 0.01). Duration of the voluntary end-expiratory apnea was not different after HSI (pre = 40 ± 5 s; post = 41 ± 4 s). MSNA responses to end-expiratory apnea were not different after HSI, expressed as an absolute change in burst frequency (n = 11; pre = 8 ± 2; post = 11 ± 1 burst/min) and as a percent increase in total activity (pre = 51 ± 4% AU; post = 53 ± 4% AU). A second group of subjects (n = 8) participated in 23-min volume/time-control intravenous isotonic saline infusions (0.9% NaCl). Isotonic saline volume-control infusions yielded no change in plasma osmolality or MSNA at rest. Furthermore, MSNA responses to apnea following isotonic saline infusion were not different. In summary, elevated plasma osmolality increased MSNA at rest and during apnea, but contrary to the hypothesis, MSNA responsiveness to apnea was not augmented. Therefore, this study does not support a neural interaction between plasma osmolality and chemoreceptor stimulation.

Rural Telehealth Team Education for Baccalaureate and Nurse Practitioner Students.

BACKGROUND: Rural areas face health care workforce shortages. Nursing students seeking rural employment require instruction and clinical experience in using telehealth to work in health care teams. METHOD: An innovative telehealth consultation simulation paired nurse practitioner (NP) students with prelicensure baccalaureate nursing degree (BSN) students. The simulation aimed to enhance NP student proficiency and confidence in telehealth consultation skills and to foster professional role development through exposure to telehealth nursing roles for RNs and NPs. On-campus BSN students assumed the role of the RN in a rural clinic and consulted with off-campus NP students using telehealth technology in the care of a standardized patient. RESULTS: Participants demonstrated level-appropriate proficiency and reported confidence in telehealth consultation and favorable attitudes toward intraprofessional communication. CONCLUSION: An intraprofessional educational model allowing BSN and NP students to develop telehealth consultation skills successfully addressed a gap in preparing nursing students to meet rural health care workforce needs. [J Nurs Educ. 2020;59(5):274-277.].

Preserved autonomic function in amenorrheic athletes.

Reproductive hormones such as estradiol and progesterone are known to influence autonomic cardiovascular regulation. The purpose of this study was to determine whether amenorrheic athletes (AA) have impaired autonomic cardiovascular regulation compared with eumenorrheic athletes (EA). Thirty-five athletes were tested: 13 AA (19 +/- 1 yr), 13 EA (21 +/- 1 yr), and 9 EA (23 +/- 1 yr) on oral contraceptives (EA-OC). Multiple indexes of autonomic cardiovascular regulation were assessed: respiratory sinus arrhythmia (RSA), cardiovagal baroreflex sensitivity (BRS) via phase IV and phase II of the Valsalva maneuver, a spontaneous index of BRS, and the heart rate and blood pressure responses to orthostatic stress (20-min 60 degrees head-up tilt). RSA was not different among the groups. There were no group differences in the spontaneous index of BRS (AA = 30 +/- 6, EA = 24 +/- 3, EA-OC = 29 +/- 5 ms/mmHg) or in phase II (AA = 8 +/- 2, EA = 7 +/- 1, EA-OC = 8 +/- 1 ms/mmHg) of the Valsalva. There was a difference in BRS during phase IV (AA = 21 +/- 3, EA = 15 +/- 1, EA-OC = 26 +/- 6 ms/mmHg; ANOVA P = 0.04). Tukey's post hoc test indicated that BRS was greater in the EA-OC group compared with the EA group (P = 0.04). There were no differences in cardiovascular responses to orthostatic stress among the groups. In conclusion, AA do not display signs of impaired autonomic function and orthostatic responses compared with EA or EA-OC during the follicular phase of the menstrual cycle.

Blood pressure and hemodynamic responses to an acute sodium load in humans.

The purpose of this study was to investigate the acute blood pressure (BP) and hemodynamic effects of sodium chloride (3% intravenous solution). Although many studies link a change in dietary sodium to a change in BP, few consider the effects of sodium concentration in the blood on BP. We hypothesized that an intravenous sodium load would increase BP, and we quantified alterations in cardiac output (Qc) and peripheral vascular resistance (PVR). Thirteen subjects (age 27 +/- 2 yr) underwent a 60-min 3% saline infusion (0.15 ml.kg(-1).min(-1)). BP was assessed on a beat-to-beat basis with a Finometer, Qc was assessed via the CO(2) rebreathing technique, and PVR was derived. Serum sodium and osmolality increased, and hematocrit declined during the infusion (ANOVA, P < 0.01). Mean arterial pressure (MAP) increased continuously during the infusion from 81.8 +/- 3.4 to 91.6 +/- 3.6 mmHg (ANOVA, P < 0.01). BP responsiveness to sodium was expressed as the slope of the serum sodium-MAP relationship and averaged 1.75 +/- 0.34 mmHg.mmol(-1).l(-1). BP responsiveness to the volume change was expressed as the slope of the hematocrit-MAP relationship and averaged -2.2 +/- 0.35 mmHg/%. The early change in MAP was mediated by an increase in Qc and the late change by an increase in PVR (P < 0.05), corresponding to a 30% increase in plasma norepinephrine. In conclusion, an acute infusion of hypertonic saline was effective in increasing BP, and both sodium and volume appear to be involved in this increase; acute BP responsiveness to serum sodium can be quantified using a MAP-sodium plot.

Sympathetic neural responses to increased osmolality in humans.

The purpose of this study was to examine the relationship between osmolality and efferent sympathetic outflow in humans. We hypothesized that increased plasma osmolality would be associated with increases in directly measured sympathetic outflow. Muscle sympathetic outflow was successfully recorded in eight healthy subjects during a 60-min intravenous hypertonic saline infusion (HSI; 3% NaCl) on one day and during a 60-min intravenous isotonic saline (ISO) infusion (0.9% NaCl) on a different day. The HSI provides an osmotic and volume stimulus, whereas the ISO infusion provides a volume-only stimulus. Muscle sympathetic nerve activity was quantified using the technique of peroneal microneurography. Plasma osmolality increased during the HSI but not during the ISO infusion (ANOVA, P < 0.05). Sympathetic outflow differed between the trials (ANOVA, P < 0.05); during the HSI burst, frequency initially increased from 14.6 +/- 2.5 to 18.1 +/- 1.9 bursts/min; during the ISO infusion, burst frequency initially declined from 14.7 +/- 2.5 to 12.0 +/- 2.1 bursts/min. Plasma norepinephrine concentration was greater at the end of the HSI compared with the end of the ISO infusion (HSI: 297 +/- 64 vs. ISO: 202 +/- 49 pg/ml; ANOVA, P < 0.05). We conclude that HSI-induced increases in plasma osmolality are associated with increases in sympathetic activity in humans.