THE RELATIONSHIP BETWEEN RATE OF VENOUS SAMPLING AND VISIBLE FREQUENCY OF HORMONE PULSES

In this paper, a stochastic model of episodic hormone secretion is used to quantify the effect of the sampling rate on the frequency of pulses that can be detected by objective computer methods in time series of plasma hormone concentrations. Occurrence times of secretion pulses are modeled as recurrent events, with interpulse intervals described by Erlang distributions. In this way, a variety of secretion patterns, ranging from Poisson events to periodic pulses, can be studied. The notion of visible and invisible pulses is introduced and the relationship between true pulses frequency and mean visible pulse frequency is analytically derived. It is shown that a given visible pulse frequency can correspond to two distinct true frequencies. In order to compensate for the `invisibility error', an algorithm based on the analysis of the original series and its undersampled subsets is proposed and the derived computer program is tested on simulated and clinical data

OBJECTIVE ASSESSMENT OF CONCORDANCE OF SECRETORY EVENTS IN 2 ENDOCRINE TIME-SERIES

A new objective method is presented for investigating the presence of a temporal relationship between episodic release of two hormones. The two time series of hormone concentrations are first analysed by an objective method for peak detection. Both data series are then transformed into quantized or discretized series by recording the occurrence of a hormone pulse as an event, characterized by the onset, the maximum, or another unique feature. The two quantized series are then matched, and the number of concordant events and discordant events are counted. Each point in series A is compared with a time-window of a selected number of points in series B, to accommodate small degree of mismatch between events in the two series. An index of concordance is computed, compensating for any spurious random coincidence: the Specific Concordance, to evaluate the frequency of concordant events in excess of those expected on the basis of chance alone. This calculation is systematically repeated, interposing a range of time-lags between the two series. A graph of Specific Concordance versus time-lag indicates the time-lag corresponding to a maximal concordance. Simulations of random series of events are performed, and their degree of concordance is evaluated in a similar fashion, thus generating frequency distributions of Specific Concordance values under the null hypothesis of no temporal relationship. This permits the selection of criteria for statistical significance at any desired p-level, for one or many lag times, and for one or multiple subjects. Various degrees of concordance can also be simulated to evaluate the performance (sensitivity, statistical power) of this approach. These methods have been implemented as a collection of short microcomputer programmes, and applied to the study of the temporal relationship between beta-endorphin and cortisol in normal subjects sampled every 10 min for 24 h. This analysis demonstrated concordance between events in the two series, with synchronous occurrence of beta-endorphin and cortisol release events significantly more frequently than expected on the basis of random association (p < 0.01)

Specific concordance index defines the physiological lag between LH and progesterone in women during the midluteal phase of the menstrual cycle.

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Specific concordance index defines the physiological lag between LH and progesterone in women during the midluteal phase of the menstrual cycle.

Using a recently developed statistically based method for assessment of the degree of concordance, we evaluated the degree of specific concordance (SC) between luteinizing hormone (LH) and progesterone secretory patterns. Eight healthy women volunteered for this study, undergoing a 12-h pulsatility study, sampling every 10 min. LH and progesterone pulse frequencies were estimated with the program DETECT (9.75 +/- 1 and 11.5 +/- 0.9 pulses/12 h, respectively; mean +/- SEM). The temporal relationship between LH and progesterone secretions was evaluated with cross-correlation analysis and with the computation of the SC index. Cross-correlation showed concordance between LH and progesterone (p less than 0.05) at a range of lag between 0 and 40 min, while the SC index indicated that LH and progesterone pulses were significantly (p less than 0.05) and maximally correlated at 10-min lag. In conclusion, our data demonstrated that the specific concordance confirms the statistically significant concordance of LH and progesterone secretory events in women during the midluteal phase. In addition, the use of this new, objective, statistically based approach permits, compared to traditional cross-correlation analysis, a more precise definition of the physiological time lag for temporal coupling of secretory events between the two hormones

Specific concordance index defines the physiological lag between LH and progesterone in women during the midluteal phase of the menstrual cycle.

Using a recently developed statistically based method for assessment of the degree of concordance, we evaluated the degree of specific concordance (SC) between luteinizing hormone (LH) and progesterone secretory patterns. Eight healthy women volunteered for this study, undergoing a 12-h pulsatility study, sampling every 10 min. LH and progesterone pulse frequencies were estimated with the program DETECT (9.75 +/- 1 and 11.5 +/- 0.9 pulses/12 h, respectively; mean +/- SEM). The temporal relationship between LH and progesterone secretions was evaluated with cross-correlation analysis and with the computation of the SC index. Cross-correlation showed concordance between LH and progesterone (p less than 0.05) at a range of lag between 0 and 40 min, while the SC index indicated that LH and progesterone pulses were significantly (p less than 0.05) and maximally correlated at 10-min lag. In conclusion, our data demonstrated that the specific concordance confirms the statistically significant concordance of LH and progesterone secretory events in women during the midluteal phase. In addition, the use of this new, objective, statistically based approach permits, compared to traditional cross-correlation analysis, a more precise definition of the physiological time lag for temporal coupling of secretory events between the two hormones