Endurance athletes have greater ventricular diastolic chamber compliance and distensibility than nonathletes and thus operate on the steep portion of their Starling curve. This may be a mechanical, nonautonomic cause of orthostatic intolerance.

Suprascapular neuropathy has often been overlooked as a source of shoulder pain. The condition may be more common than once thought as it is being diagnosed more frequently. Etiologies for suprascapular neuropathy may include repetitive overhead activities, traction from a rotator cuff tear, and compression from a space-occupying lesion at the suprascapular or spinoglenoid notch. Magnetic resonance imaging is useful for visualizing space-occupying lesions, other pathological entities of the shoulder, and fatty infiltration of the rotator cuff. Electromyography and nerve conduction velocity studies remain the standard for diagnosis of suprascapular neuropathy; however, data on interobserver reliability are limited. Initial treatment of isolated suprascapular neuropathy is typically nonoperative, consisting of physical therapy, nonsteroidal anti-inflammatory drugs, and activity modification; however, open or arthroscopic operative intervention is warranted when there is extrinsic nerve compression or progressive pain and/or weakness. More clinical data are needed to determine if treatment of the primary offending etiology in cases of traction from a rotator cuff tear or compression from a cyst secondary to a labral tear is sufficient or whether concomitant decompression of the nerve is warranted for management of the neuropathy.

We evaluated regional electrical impedance (Z degree) at 2.5 and 100 kHz to separate intra- and extracellular fluid changes and correlated Z degree over the thorax (TI) to relative changes in the central blood volume (CBV) induced by head-up tilt. In nine experiments head-up tilt resulted in normotensive central hypovolaemia associated with a 3.7 +/- 0.4 Ohm (mean +/- SE) increase in TI100 kHz after 60 min. In 24 experiments pre-syncopal symptoms were induced after 43 +/- 2 min, when TI100 kHz had increased 4.2 +/- 0.2 Ohm. Head-up tilt instantly decreased the activity of technetium labelled erythrocytes (99Tcm) over the thorax by 24 +/- 2%, and increased 99Tcm over the thigh by 68 +/- 10% (P less than 0.01, n = 8) with no further changes during the sustained tilt. Haematocrite increased during head-up tilt from 43.1 +/- 0.3 to 47.9 +/- 0.6% (P less than 0.01, n = 8). Accordingly, the increase in TI (6.3 +/- 0.6 vs. 4.5 +/- 0.4 Ohm, n = 6) and the decrease in Z degree through one leg (7.2 +/- 1.2 vs. 2.8 +/- 0.5 Ohm, n = 6) at 2.5 kHz was more pronounced than at 100 kHz. Also the changes in TI were correlated to CBV as calculated from 99Tcm and haematocrite (r = 0.90, P less than 0.01). The results suggest that: (1) Hypovolaemic shock is associated with a faster increase of TI than normotensive head-up tilt. (2) Head-up tilt is characterized by an initial decrease in CBV followed by a further decrease in plasma volume, which eventually leads to hypovolaemic shock. (3) Blood volume changes during head-up tilt are reflected in regional Z degree.

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