Impedance and relative displacements of relaxed chest wall up to 4 Hz

We measured the effective resistance (Reff) and elastance (Eeff) of the chest wall in four subjects, relaxed at functional residual capacity (FRC), during sinusoidal volume changes (5% vital capacity up to 4 Hz) delivered at the mouth. Subjects sat in a head-out body plethysmograph, and transthoracic pressure was measured with an esophageal balloon. Changes in Reff and in Eeff with frequency were nearly the same in all subjects. Reff (in cmH2O X l-1 X s) was 2.9 +/- 0.8 at 0.2 Hz and fell sharply to minimum values (0.5-0.9) at 1-4 Hz. Eeff (in cmH2O X l-1) increased from approximately 10 at the lowest frequency to a plateau of about 15 at 1-3 Hz and decreased above 3 Hz. In the same subjects, we measured the relative magnitude and phase between the displacements of different parts of the chest wall with magnetometers during identical sinusoidal forcing. Results indicate that the chest wall expands and deflates uniformly at frequencies up to 1 Hz. Thereafter the abdomen makes relatively larger excursions, and the relative magnitude and phase of displacement at different points on the chest wall show complex changes. We conclude that the frequency dependence of Reff and Eeff below 1 Hz is not due to nonuniformities in displacement of different parts of the chest wall. The frequency dependency of Reff is consistent with an increasing contribution of rate-independent plastic dissipation to the pressure difference in phase with flow as breathing frequency decreases.     

Membrane filtration method for bacteriological testing of water: enhanced colony visualization and stability on purification of phenol red indicator

Commercially-available phenol red indicator, purified by adsorption chromatography was incorporated into lauryl sulphate broth (LSB) used in the membrane filtration method for the detection of Escherichia coli and other coliform bacteria. Relative to LSB containing the impure dye or its major contaminant, the purified phenol red provided clear visualization of discrete yellow colonies observed against a white background. The colonies remained stable for at least 24 h at 25°C under standard laboratory lighting conditions. This simple procedure will enhance the detection of coliforms in samples.     

Isolation and complete nucleotide sequence of the gene for bovine parathyroid hormone

The structure of the bovine parathyroid hormone (PTH) gene has been analyzed by Southern blot hybridization of genomic DNA and by nucleotide sequence analysis of a cloned PTH gene. In the Southern analysis, several restriction enzymes produced single fragments that hybridized to PTH cDNA suggesting that there is a single bovine PTH gene. The restriction map of the cloned gene is the same as that determined by Southern blot analysis of bovine DNA. The sequence of 3154 bp of the cloned gene has been determined including 510 bp and 139 bp in the 5' and 3' flanking regions, respectively. The gene contains two introns which separate three exons that code primarily for: (i) the 5' untranslated region, (ii) the pre-sequence of preProPTH, and (iii) PTH and the 3' untranslated region. The gene contains 68% A + T and unusually long stretches of 100- to 150-bp sequences containing alternating A and T nucleotides in the 5' flanking region and intron A. The 5' flanking region contains two TATA sequences, both of which appear to be functional as determined by S1 nuclease mapping. Compared to the rat and human genes, the locations of the introns are identical but the sizes differ. Comparable human and bovine sequences in the flanking regions and introns are about 80% homologous.     

Abdominal muscle use during quiet breathing and hyperpnea in uninformed subjects

Although there is electromyographic evidence for abdominal muscle activity during quiet breathing in standing subjects, several studies have shown, or assumed, that subjects normally breathe on their relaxation characteristics. This latter observation would by itself suggest that abdominal muscles do not contract during quiet breathing. To test this assumption we observed abdominal and rib cage displacements with magnetometers in 17 uninformed subjects. During quiet breathing most subjects showed evidence of tonic or phasic abdominal muscle contraction while standing and sitting but not supine. Subjects studied during hyperpnea immediately following exercise-showed evidence of greater abdominal muscle contraction than at rest. We conclude that most subjects standing at rest normally contract their abdominal muscles.