Heart rate variability and hemodynamic alterations in canines with normal cardiac function during exposure to pressure support, continuous positive airway pressure, and a combination of pressure support and continuous positive airway pressure.

Variations in intrathoracic pressure generated by different ventilator weaning modes may significantly affect intrathoracic hemodynamics and cardiovascular stability. Although several investigators have attributed cardiovascular alterations during ventilator weaning to augmented sympathetic tone, there is limited investigation of changes in autonomic tone during ventilator weaning. Heart rate variability (HRV), the analysis of beat-to-beat changes in heart rate, is a noninvasive indicator of autonomic tone that might be useful in the identification of patients who are at risk for weaning difficulty due to underlying cardiac dysfunction. The authors describe HRV and hemodynamics in response to 3 ventilatory conditions: pressure support (PS) 10 cmH2O, continuous positive airway pressure (CPAP) 10 cmH2O, and a combination of PS 10 cmH2O and CPAP 10 cmH2O (PS + CPAP) in a group of canines with normal ventricular function. Six canines were studied in the laboratory. Continuous 3-lead electrocardiographic data were collected during baseline (controlled mechanical ventilation) and following transition to each of the ventilatory conditions (PS, CPAP, PS + CPAP) for analysis of HRV. HRV was evaluated using power spectral analysis to define the power under the curve in a very low frequency range (0.0033 to < 0.04 Hz, sympathetic tone), a low frequency range (0.04 to < 0.15 Hz, primarily sympathetic tone), and a high frequency range (0.15 to < 0.40 Hz, parasympathetic tone). A thermodilution pulmonary artery catheter measured cardiac output and right ventricular end-diastolic volume to describe global hemodynamics. There were significant increases in very low frequency power (sympathetic tone) with a concomitant significant reduction in high-frequency power (parasympathetic tone) with exposure to PS + CPAP. These alterations in HRV were associated with significantly increased heart rate and reduced right ventricular end-diastolic volume. Although there was a small but significant increase in cardiac output with exposure to PS, HRV was unchanged. These data indicate that there was a relative shift in autonomic balance to increased sympathetic and decreased parasympathetic tone with exposure to PS + CPAP. The increase in intrathoracic pressure reduced right ventricular end-diastolic volume (preload). This hemodynamic alteration generated a change in autonomic tone, so that cardiac output could be maintained. Individuals with autonomic and/or cardiovascular dysfunction may not be capable of this type of response and may fail to successfully wean from mechanical ventilation.

Comparison of anxiety assessments between clinicians and patients with acute myocardial infarction in cardiac critical care units.

BACKGROUND: Although anxiety is common after acute myocardial infarction and can adversely affect physical recovery, it is not part of the routine clinical assessment of patients with myocardial infarction. Furthermore, evidence suggests that patients and clinicians differ significantly in their assessments of patients' anxiety levels. OBJECTIVES: To determine the extent to which clinicians assess anxiety in patients with acute myocardial infarction and to compare patients' self-ratings with their clinicians' assessments. METHODS: In a prospective, descriptive study, 101 patients used the Spielberger State Anxiety Index to assess their anxiety during the first 48 hours after admission for acute myocardial infarction. Patients' scores were compared with nurses' and physicians' assessments of the patients' anxiety as reported in the medical record. RESULTS: Only 45 patients (45%) had anxiety assessments noted in the record. Of those 45, 26 patients (58%) were described simply as anxious without any further description of the level of anxiety. Eleven (24%) of those 45 patients had behaviors of anxiety recorded, again without any indication of the level of anxiety. No association between patients' self-assessments and their clinicians' assessments was apparent (lambda = .03; P > .05). CONCLUSIONS: Anxiety was not routinely assessed, despite nearly half the patients reporting moderate to extreme anxiety when asked. When clinicians assessed anxiety, their assessments did not match patients' self-ratings of anxiety. A simple, easy-to-use instrument for discriminating levels of anxiety is needed.

Cardiac power output during transition from mechanical to spontaneous ventilation in canines.

Hemodynamic instability during weaning from mechanical ventilation is one proposed cause of weaning failure. This study evaluated cardiac power output (CPO) as an indicator of significant hemodynamic alteration and cardiac reserve during the transition from controlled mechanical ventilation to spontaneous ventilation using three clinical weaning modes. It also compared CPO with commonly used indicators of hemodynamic instability during weaning. The data suggest that CPO is a sensitive indicator of significant hemodynamic alteration and could be used to optimize cardiovascular function during weaning from mechanical ventilation to increase the likelihood of weaning success. Key words: cardiac output, cardiac power output, hemodynamic monitoring, mechanical ventilation

Cloning of the 16-kDa V-ATPase proteolipid subunit from the red imported fire ant Solenopsis invicta buren (Hymenoptera: Formicidae).

V-ATPases are ubiquitous proton pumps found in eukaryotes, and are important in regulating the pH of cell compartments and in creating membrane potentials. The V-ATPase creates a proton gradient that is used as an energy source for the transport of other ions. The 16-kDa proteolipid is the proton-translocating subunit c of V-ATPases. Using PCR methods, we have cloned the fire ant 16-kDa subunit c, providing the first molecular characterization of this protein in a social insect. Northern blot analysis revealed three possible different transcripts. The presence of V-ATPases in ant Malpighian tubules had been previously demonstrated, where they provide the proton gradient necessary for the excretion of other ions and the formation of primary urine. The 16-kDa proteolipid is highly conserved among insects, and in ants may be important to the critical processes of diuresis and olfaction as a key component of the V-ATPase. Arch.

A comparison of hemodynamic changes during the transition from mechanical ventilation to T-piece, pressure support, and continuous positive airway pressure in canines.

The immediate transition from positive pressure mechanical ventilation to spontaneous ventilation may generate significant cardiopulmonary hemodynamic alterations based on the mode of weaning selected, particularly in individuals with preexisting cardiac dysfunction. The purpose of this study was to compare hemodynamic responses associated with the initial transition to 3 modes of ventilator weaning (spontaneous ventilation/T-piece, pressure support [PS], and continuous positive airway pressure [CPAP]). Right ventricular hemodynamic responses were evaluated with a thermodilution pulmonary artery catheter; while left ventricular hemodynamic responses were measured by a transducer-tipped Millar catheter and conductance catheter. Two groups of canines were studied. Group 1: normal biventricular function (n = 10) and group 2: propranolol-induced biventricular failure (n = 10). Dependent variables were measured at baseline on controlled mechanical ventilation (MV) and following the initial transition to each of 3 randomized spontaneous ventilatory conditions: T-piece, PS 5 cmH2O, and CPAP 5 cmH2O. Both groups significantly increased cardiac output in response to T-piece. Right ventricular stroke work was also significantly increased with T-piece and CPAP in both groups of subjects. Left ventricular response depended on baseline ventricular function. Baseline ventricular function influenced hemodynamic response to the immediate transition from mechanical to spontaneous ventilation. There were also differential hemodynamic responses based on the ventilatory mode. Consideration of baseline cardiac function may be an important factor in the selection of an appropriate mode of spontaneous ventilation following controlled MV.

Diagnosing and treating primary pulmonary hypertension.

Primary pulmonary hypertension (PPH) is a pulmonary vascular disease characterized by an elevation in mean pulmonary artery pressure and pulmonary vascular resistance. Recently, PPH gained national attention because of its association with appetite suppressants. PPH may also be associated with pregnancy, hypothyroidism, autoimmune disorders, human immunodeficiency virus infection, and the use of drugs such as oral contraceptives and cocaine. Patients with PPH may report dyspnea on exertion and fatigue. Early diagnosis is crucial. New therapeutic regimens have dramatically reduced mortality rates and improved quality of life by halting the progression of pulmonary vascular remodeling and averting right-sided heart failure. These therapies include high-dose calcium channel antagonists, anticoagulants, and continuous intravenous prostacyclin. Lung or heart-lung transplantation remains a viable therapeutic option for patients who are treated late in the disease process, who are not responsive to medical management, or who remain symptomatic and continue to deteriorate.

Neurohormonal responses during positive pressure mechanical ventilation.

Positive pressure mechanical ventilation is used daily in critical care units to support ventilation and improve oxygenation in critically ill patients. One adverse response to positive pressure mechanical ventilation is a reduction in urinary output and sodium and water retention. This consequence is attributed to complex neurohormonal responses intended to maintain hemodynamic homeostasis. This article reviews the physiologic nature of these responses and research findings related to these responses and provides clinicians with information about the importance of these responses, particularly in patients with underlying cardiac dysfunction.

The role of the critical care nurse in preventing heart failure after acute myocardial infarction.

Heart failure is a disabling, progressive, and highly lethal condition. This profile makes it an ideal target for preventative strategies. Critical care nurses caring for cardiac patients must be aware of these strategies so that they can effectively assess patient risk and intervene as an educator and advocate for appropriate treatment.

Cardiac patients' conversations and the process of establishing meaning.

The purpose of this study was to describe and analyze the naturally occurring conversations of hospitalized cardiac patients. According to Blumer's symbolic interactionist perspective, individual interpretation or the meaning of a stressful event is developed and shared through social interaction. The meaning of an event is the foundation for behavioral responses that can promote or impede recovery. This study analyzed the naturally occurring conversations of ten cardiac patients. Three themes were identified within these conversations. The first theme, labeled finding cause, incorporated the processes of structuring the illness event, determining a cause for the event, and sharing the story of the illness with someone. The second theme, labeled acting normally, included participants attempting to preserve their normal patterns or habits, to resume normal activities, and to maintain personal control. The third theme, labeled passing time, encompassed sequencing the experiences within the illness event and hospitalization, waiting for news about their condition and/or recovery and structuring their future following recovery from the acute illness. An analysis of naturally occurring conversation can expedite recognition of the processes cardiac patients use to structure their reality and determine the meaning of an illness event. This may provide a foundation for understanding behaviors that affect physiological and psychosocial recovery.