Apnea training and physiological responses

A study that might be of interest, concerning apnea training and physiological responses in "apnea-untrained" subjects:
Effects of two weeks of daily apnea t... [Scand J Med Sci Sports. 2011] - PubMed - NCBI

Abstract
Three potentially protective responses to hypoxia have been reported to be enhanced in divers: (1) the diving response, (2) the blood-boosting spleen contraction, and (3) a long-term enhancement of hemoglobin concentration (Hb). Longitudinal studies, however, have been lacking except concerning the diving response. Ten untrained subjects followed a 2-week training program with 10 maximal effort apneas per day, with pre- and posttraining measurements during three maximal duration apneas, and an additional post-training series when the apneic duration was kept identical to that before training. Cardiorespiratory parameters and venous blood samples were collected across tests, and spleen diameters were measured via ultrasound imaging. Maximal apneic duration increased by 44 s (P < 0.05). Diving bradycardia developed 3 s earlier and was more pronounced after training (P < 0.05). Spleen contraction during apneas was similar during all tests. The arterial hemoglobin desaturation (SaO(2)) nadir after apnea was 84% pretraining and 89% after the duration-mimicked apneas post-training (P < 0.05), while it was 72% (P < 0.05) after maximal apneas post-training. Baseline Hb remained unchanged after training, but reticulocyte count increased by 15% (P < 0.05). We concluded that the attenuated SaO(2) decrease during mimic apneas was due mainly to the earlier and more pronounced diving bradycardia, as no enhancement of spleen contraction or Hb had occurred. Increased reticulocyte count suggests augmented erythropoiesis.

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Ulf said:

Do you know how they determined the break point and how early the bradycardia developed?

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At the beginning of apnea (often initial 10-20 sec) you usually see a peak in heart rate. The following is stated in the paper:
"To analyze the onset of HR reduction from the initial tachycardia, the time from apnea initiation to HR peak was measured by visual inspection of the individual HR/time relationship by an observer blinded to the performance results."

It is difficult to determine the time exactly from the graph that is given in the paper (Fig 3) but I would say the peak occurred at ca 20-25 sec after initiation of apnea before training, and at ca 15-20 sec after training.

Does this mean that that you could expect an increase in HB if they had continued for more than two weeks or does the apnea simply "consume" HB?

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I guess (have no direct proof) that Hb could have increased had the training continued for longer.

could it be that it takes more than two weeks to develop enhanced spleen contraction?

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Yes. But it may also be that this is a response that is not "trainable" (even though I tend to doubt that). Another quotation from the paper:
"Spleen contraction and Hb increase were observed both before and after training, but to the same extent..."
"This study therefore suggests that the previously observed large spleen volumes and augmented spleen contraction observed in trained apnea divers (Bakovic et al., 2003; Richardson et al., 2005; Prommer et al., 2007; Schagatay et al., 2007b) may either reflect predisposition, or that such effects require longer periods of training or perhaps a more significant training intensity or load. Apneic training history and apneic durations were considerably longer in previous studies of spleen function in trained divers. Further studies concerning these effects may require at least several months of intense apnea training before the possibility of a trainable spleen can be ruled out."