Effect of lung volume on ventilation distribution

To examine the effect of preinspiratory lung volume (PILV) on ventilation distribution, we performed multiple-breath N2 washouts (MBNW) in seven normal subjects breathing 1-liter tidal volumes over a wide range of PILV above closing capacity. We measured the following two independent indexes of ventilation distribution from the MBNW: 1) the normalized phase III slope of the final breaths of the washout (Snf) and 2) the alveolar mixing efficiency during that portion of the washout where 80-90% of the lung N2 had been cleared. Three of the subjects also performed single-breath N2 washouts (SBNW) by inspiring 1-liter breaths and expiring to residual volume at PILV = functional residual capacity (FRC), FRC + 1.0, and FRC - 0.5, respectively. From the SBNW we measured the phase III slope over the expired volume ranges of 0.75-1.0, 1.0-1.6, and 1.6-2.2 liters (S0.75, S1.0, and S1.6, respectively). Between a PILV of 0.92 +/- 0.09 (SE) liter above FRC and a PILV of 1.17 +/- 0.43 liter below FRC, Snf decreased by 61% (P less than 0.001) and alveolar mixing efficiency increased from 80 to 85% (P = 0.05). In addition, Snf and alveolar mixing efficiency were negatively correlated (r = 0.74). In contrast, over a similar volume range, S1.0 and S1.6 were greater at lower PILV. We conclude that, during tidal breathing in normal subjects, ventilation distribution becomes progressively more inhomogeneous at higher lung volumes over a range of volumes above closing capacity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prenatal prevention of drepanocytosis: analysis of cellular DNA in 2 cases

Direct analysis of fetal DNA using restriction endonucleases constitutes a major area of progress in prenatal diagnosis. This recent technology may permit the precise identification of a mutant allele for some diseases, whereas in others it allows the familial segregation of a pathogenic allele to be followed by its linkage to a DNA sequence polymorphism. This type of analysis, available in a few centers, is currently used, among others, for the prenatal diagnosis of hemoglobinopathies such as sickle cell anemia. After fetal cells have been obtained by choriocentesis or amniocentesis, the extracted DNA is exposed to selected restriction enzymes. In the diagnosis of sickle cell anemia the mutant codon responsible for the substitution of glutamic acid by valine in the beta hemoglobin chain is no longer cut by the enzyme Mst II, due to its variance with the normal codon; this difference in fragment length is detected by DNA electrophoresis, and the particular fragments are identified by molecular hybridization with appropriate radioactive probes. Utilizing these methods the genotype of a homozygous normal fetus can be distinguished from that of a homozygote affected or a heterozygote for the sickle mutation of the beta hemoglobin chain. We have recently applied this prenatal methodology to the pregnancies of two couples from Zaire, in which each member was a proven sickle cell carrier. Fetal material was obtained in both cases by amniocentesis at the 16th week of gestation and followed by cell culture. In the first case, a 46, XX fetus, DNA (10 mcg) revealed a heterozygous sickle cell carrier genotype.(ABSTRACT TRUNCATED AT 250 WORDS)     

Visual perception: mind and brain see eye to eye

Recent functional imaging studies have identified neural activity that is closely associated with the perception of illusory motion. The mapping of the mind onto the bin appears to be one-to-one: activity in visual 'motion area' MT is highly correlated with perceptual experience.