Nonlinear measures of heart rate time series: influence of posture and controlled breathing

In this study, we investigated measures of nonlinear dynamics and chaos theory in regards to heart rate variability in 27 normal control subjects in supine and standing postures, and 14 subjects in spontaneous and controlled breathing conditions. We examined minimum embedding dimension (MED), largest Lyapunov exponent (LLE) and measures of nonlinearity (NL) of heart rate time series. MED quantifies the system's complexity, LLE predictability and NL, a measure of deviation from linear processes. There was a significant decrease in complexity (P < 0.00001), a decrease in predictability (P < 0.00001) and an increase in nonlinearity (P = 0.00001) during the change from supine to standing posture. Decrease in MED, and increases in NL score and LLE in standing posture appear to be partly due to an increase in sympathetic activity of the autonomous nervous system in standing posture. An improvement in predictability during controlled breathing appears to be due to the introduction of a periodic component.

Expression of epidermal and transforming growth factors in pancreatic cancer

Pancreatic cancer continues to be a major clinical problem and little is known of the various cellular and molecular events associated with this malignancy. Growth factors and their receptors have important functions in the process of tumor progression. We have examined by immunocytochemistry, the expression of epidermal growth factor (EGF), its receptor (EGFR) and the transforming growth factors alpha and beta (TGF alpha and beta) in various grades of pancreatic adenocarcinoma. Expression of the growth factors was compared to their distribution in apparently normal pancreas and chronic pancreatitis. EGF, TGF alpha and TGF beta was expressed in normal pancreatic tissue while the expression of EGFR was slight and restricted. In chronic pancreatitis, this expression of EGFR increased and was found to be moderate in intensity. Expression of EGF, TGF alpha and TGF beta was similar to that seen in normal pancreas. Moderate to intense expression of EGF and TGF alpha was evident in all grades of pancreatic cancer. Expression of EGFR was intense in all these lesions. However, the most significant finding was the absence of TGF beta in all pancreatic cancer lesions. These results may have significant implications for pancreatic tumor progression. EGF and TGF alpha are growth promoters influencing the expression of EGFR. TGF beta, on the other hand exerts an anti-proliferative effect and favours differentiation. It therefore appears that the balance between EGF and TGF alpha on the one hand and TGF beta on the other may be critical in the process of tumor progression, especially if one considers chronic pancreatitis as a pre-malignant condition and the growth factor expression associated with it.