Feasibility of bedside thoracic ultrasound in the helicopter emergency medical services setting.

INTRODUCTION: Bedside thoracic ultrasound has been shown to be a valuable diagnostic tool in the emergency department. The purpose of this study was to evaluate the feasibility of bedside thoracic ultrasound in the prehospital HEMS setting. SETTING: Air ambulance helicopters during patient transportation. METHODS: This was a prospective pilot study. 71 consecutive, nonpregnant patients over 18 years old were enrolled. While in flight, providers completed limited bedside thoracic ultrasounds with the patient supine and recorded their interpretation of the presence or absence of the ultrasonographic sliding lung sign on a closed data-set instrument. RESULTS: 41 (58%) of the eligible patients had a recorded thoracic ultrasound acquired in flight. The level of agreement in image interpretation between the flight crew and expert reviewer was substantial (Kappa 0.67, CI 0.44-0.90). The reviewer rated 54% of all images as "good" in quality. The most common reason cited for not completing the ultrasound was lack of enough provider time or space limitations within the aircraft cabin. CONCLUSION: The results of this study suggest that, with limited training, bedside thoracic ultrasound image acquisition and interpretation for the sliding lung sign in the HEMS setting is feasible.

Effect of position and weight force on inferior vena cava diameter--implications for arrest-related death.

INTRODUCTION: The physiology of many sudden, unexpected arrest-related deaths (ARDs) proximate to restraint has not been elucidated. A sudden decrease in central venous return during restraint procedures could be physiologically detrimental. The impact of body position and applied weight force on central venous return has not been previously studied. In this study, we use ultrasound to measure the size of the inferior vena cava (IVC) as a surrogate of central venous return in the standing position, prone position, and with weight force applied to the thorax in the prone position. METHODS: This was a prospective, observational study of volunteer human subjects. The IVC was visualized from the abdomen in both the longitudinal and transverse section in the standing and prone positions without weight force applied, and with 100 lbs (45 kg) and 147 lbs (67 kg) of weight force on the upper back in the prone position. Maximum and minimum measurements were determined in each section to account for possible respiratory variation of the IVC. RESULTS: The IVC significantly decreased in size with each successive change: from standing to prone, from prone to prone with 100 lbs (45 kg) weight compression, from prone with 100 lbs (45 kg) weight compression to prone with 147 lbs (67 kg) weight compression (p < 0.0001). The vital sign measurements had no statistical change. CONCLUSIONS: The physiology involved in many sudden, unexpected ARDs has not been elucidated. However, in our study, we found a significant decrease in IVC diameter with weight force compression to the upper thorax when the subject was in the prone position. This may have implications for the tactics of restraint to aid in the prevention of sudden, unexpected ARD cases.

Synchronicity of frequently sampled thyrotropin (TSH) and leptin concentrations in healthy adults and leptin-deficient subjects: evidence for possible partial TSH regulation by leptin in humans.

Leptin signals the status of energy reserves to the brain. Leptin stimulates biosynthesis of TRH in vitro and influences the activity of the hypothalamic-pituitary-thyroid axis in vivo in rodents. Because blood levels of both leptin and TSH display diurnal variation with a distinct nocturnal rise, we sought to determine whether a relationship exists between fluctuations in circulating leptin and TSH. We measured serum leptin and TSH levels every 7 min for 24 h in five healthy men and found that both leptin and TSH levels are highly organized and pulsatile. A similar pattern of leptin and TSH rhythms was observed, with TSH and leptin levels reaching a nadir in late morning and a peak in the early morning hours. Importantly, cosinor analysis on the absolute leptin and TSH levels revealed a statistically significant fit for a 24-h period and the two hormones showed similar probabilities of rhythm and superimposable peak values. Furthermore, this study shows a strong positive Pearson correlation between the 24-h patterns of variability of leptin and TSH in healthy subjects. Finally, the ultradian fluctuations in leptin levels showed pattern synchrony with those of TSH as determined by cross-correlation analysis, by cross-approximate enthropy and Bayessian analysis applied independently. To further explore whether these associations could reflect an underlying regulation of TSH secretion by leptin, we also studied frequently sampled leptin and TSH levels in four brothers, members of a family with leptin deficiency (one normal homozygote, two heterozygotes, and one leptin-deficient homozygote). Leptin levels of the homozygous leptin-deficient subject are detectable but bioinactive, and the rhythm of his TSH is disorganized. 24-h pattern of leptin and TSH variability in the heterozygous subjects, although significantly correlated, showed a weaker correlation compared with the strong correlation in the normal subjects. These data are consistent with the possibility that leptin may regulate TSH pulsatility and circadian rhythmicity, but interventional studies are needed to definitively prove whether leptin regulates the minute-to-minute oscillations and ultradian rhythm of TSH levels.

Seasonal variation in core temperature regulation during sleep in patients with winter seasonal affective disorder.

Nocturnal core temperature during sleep is elevated during depression compared with remission in nonseasonally depressed patients. Similarly, nocturnal core temperature is higher during winter depression compared with remission induced by light treatment in seasonal affective disorder (SAD) patients. We investigated whether nocturnal core temperature in SAD patients naturally becomes lower in summer (during remission) compared with winter (during depression). Twenty-four-hour core temperature profiles were obtained in winter and summer in 22 SAD patients and 22 controls. The nocturnal core temperature minima were lower in summer compared with winter in SAD patients (p < .005), but not controls (p > .4). The seasonal changes in nocturnal core temperatures in SAD patients may reflect a unique physiological responsiveness of SAD patients to the change of seasons, and may be intimately related to the seasonal disturbances of mood and energy that are characteristic of SAD.