Michael K. Loushin

An improved method for muscle force assessment in neuromuscular disease.

We describe here the reliability and validity of methods to quantify involuntary muscle torque induced by non-invasive nerve stimulation. A rigid apparatus was used to hold the subjects limb in a predetermined position and confine movement to a specific direction (i.e. ankle dorsiflexion or thumb adduction). An incorporated strain gauge was used to measure isometric torque, and all data were recorded by a data acquisition program. The innervating nerves were stimulated by surface electrodes, using either single stimuli to generate a twitch, or short trains of stimuli to produce tetanic contraction of the individual muscle under study. The average peak tetanic torque generated by the dorsiflexor muscles in healthy control was 20.4 +/- 3.8 Nm and varied by 3.7% with repeated testing. The mean torque generated by the adductor pollicis muscle in controls was 1.5 +/- 0.4 Nm and varied by 4.6% with repeated testing. In patient populations significant changes in activated torque were readily quantified, and the effects of treatment can be easily assessed. Furthermore, several specific parameters of recorded isometric contractions were measured; e.g. time between stimulus and torque onset, peak rate of torque development, time to peak torque, half-relaxation time, and others (none of which are measurable when using voluntary contraction of muscle). Compared to current assessment methods, monitoring muscle torque generated by nerve stimulation improves objectivity, reliability, and quantitative capabilities. The presented method has significant potential both in diagnosing neuromuscular disorders and determining treatment efficacy.

The Effects of Anesthetic Agents on Cardiac Function

Today, anesthesia is considered necessary for many types of surgeries and procedures. In general, anesthesia may provide analgesia, amnesia, hypnosis, and muscle relaxation. The depth of administered anesthesia can vary from minimal sedation to general anesthesia (Table 1). General anesthesia typically causes significant alterations in hemodynamics, especially during induction of anesthesia. Importantly, both inhalational and intravenous anesthetics can affect cardiovascular performance; this includes effects on cardiac output, heart rate, systemic vascular resistance, cardiac conduction system, myocardial contractility, coronary blood flow, or blood pressures. Yet, the choice of inhalational and intravenous anesthetics is typically associated with the patient’s underlying cardiovascular status, such as the presence of heart failure and hypovolemia. The primary goal of this chapter is to make commonly employed methodologies and anesthetics more familiar to the reader, with particular attention to the potential influences on the cardiovascular system.

A Delayed Cardiopulmonary Reaction to an Intravenous Immunosuppressant Thymoglobulin After Pancreas Transplant

IMPLICATIONS Adverse cardiopulmonary reaction to an intravenous immunosuppressant after solid organ transplantation might not be evident immediately in the postoperative period and might result in serious cardiopulmonary compromise.

The Effects of Temperature on Cardiac Pacing Thresholds

Background:  Human core body temperature can fluctuate between 36°C (sleep) and 42°C (intense exercise). Also, efforts are underway to develop implantable pacing systems that minimize heating during magnetic resonance imaging (MRI) scans (i.e., MRI safe). Concerns exist that ventricular pacing capture thresholds (VPCT) are modified by changing cardiac temperatures. This project was designed to assess the effects of temperature on VPCT of the mammalian heart.

Intrathoracic pressure regulation to treat intraoperative hypotension: A phase II pilot study.

BACKGROUND Intraoperative hypotension secondary to acute blood loss and fluid shifts increases morbidity and mortality. Intrathoracic pressure regulation (IPR) is a new therapy that enhances circulation by increasing venous return with a negative intrathoracic pressure created noninvasively, either actively (vacuum source or patient inspiration) or passively (chest recoil during cardiopulmonary resuscitation). OBJECTIVE In this Phase II pilot study, we tested the hypothesis that active IPR therapy would improve the haemodynamic status of patients who developed clinically significant hypotension during abdominal surgery. DESIGN A phase II, single cohort, interventional pilot study. SETTING University of Minnesota Fairview Hospital. PATIENTS Twenty-two patients [American Society of Anesthesiologists (ASA) physical status I to III] were enrolled prospectively of whom 15 experienced intraoperative hypotension. INTERVENTION If intraoperative hypotension occurred more than 10 min after induction, the IPR device was applied immediately for a minimum of 10 min. MAIN OUTCOME MEASURE The hypotensive SBP immediately before the start of IPR treatment was compared with the SBP obtained at the end of IPR therapy. The paired Students t-test was used to determine statistical significance (P < 0.05). RESULTS Fifteen of the 22 patients enrolled experienced 18 hypotensive episodes, which were treated with at least 10 min of IPR therapy. Fourteen episodes responded to IPR alone and four episodes (four patients) required additional fluid and vasopressor therapy to treat the hypotension. The group mean ± SD SBPs at the onset of the IPR treatment and at the end of IPR treatment were 90.7 ± 9.7 and 98.4 ± 17.4 mmHg (P = 0.02), respectively. The maximum SBP reached during the treatment was 105.6 ± 19.6 mmHg. Pulse pressure increased from 36.8 ± 8.5  mmHg immediately before IPR treatment to 41.5 ± 11.1 mmHg (P = 0.02) at the end of IPR treatment. Mean arterial pressure (MAP) increased from 66.3 ± 9.4 mmHg immediately before IPR treatment to 71.5 ± 14.4 mmHg (P = 0.03) at the end of IPR treatment. No adverse events were identified with use of the IPR device. CONCLUSION IPR may be useful in treating intraoperative hypotension without additional fluid or vasopressor therapy. No significant adverse events were observed. On the basis of this phase II pilot study, a larger study is justified.

The Path of a Pulmonary Artery Catheter Visualized through a Beating Human Heart

Pulmonary artery (PA) catheters can be positioned within a patient via access through the right side of the heart, for diagnostic and monitoring purposes. Data obtained include PA, right atrial, and left atrial pressures, cardiac outputs, and samples of mixed venous blood. Such catheters are typically placed with the aid of their distal inflatable balloon and by sensed catheter pressures—thus, placed without fluoroscopy. Here we obtained novel videoscopic imaging of a PA catheter insertion by employing visible heart methodologies (1). Specifically, in a reanimated, nonviable donor human heart (male, 45 yr old), eliciting a native sinus rhythm, functioning in a fourchamber working mode, the use of a clear perfusate allowed for this visualization, while fluoroscopic images were also captured concurrently (not continuously). Note that the catheter’s balloon was filled with fluoroscopic contrast to enhance visualization (see video in the online supplement). Associated pressure tracings and computer animations were synchronized appropriately with the catheter delivery. Of note, the “wedge“ pressure, defined as a drop in pressure when the balloon totally occludes the PA (Figure 1), was simulated by partially ligating a distal portion of this heart’s remaining PA (i.e., this was near the outflow cannula, thus the wedge position appears much more proximal than would be found in vivo, which would be within a lung). See also the Pulmonary Artery Catheter Education Project (www.pacep.org) for additional theoretical and educational information.

Mechanical Aspects of Cardiac Performance

Monitoring of hemodynamic and mechanical parameters of the heart are reviewed. Clinical methodologies are discussed along with tools used in a research setting. Specifically, these include: arterial blood pressure, central venous pressure, pulmonary artery pressure, mixed venous oxygen saturation, cardiac output, pressure–volume loops, flow monitoring, and Frank–Starling curves. These parameters are monitored using technology such as pressure transducers, Swan–Ganz catheters, thermodilution, sonomicrometry crystals, conductance catheters, ultrasound transducers, and loop recorders.