Application of chaos theory to a model biological system: Evidence of self-organization in the intrinsic cardiac nervous system

The neural organization that determines the specific beat-to-beat pattern of cardiac behavior is expected to be demonstrated in the independent regulation of the RR intervals (chronotropy) and the corresponding QT subintervals (inotropy), as the former defines the rate of contraction and the latter has a linear negative correlation with the peak pressure inside the contracting ventricular muscles. The neurons of the isolated cardiac nervous system, many of which are located in the fat-pads of the heart, exhibit the same types of mechanical and chemical receptors and the same types of cholinergic and noradrenergic effectors as those found in the neural superstructure. In the surgically isolated and perfused rabbit heart we studied the responses of the QT and RR intervals evoked by block of coronary blood flow. We found that if we separated each RR cycle into QT and RR-QT components, then the dynamics of variation for each subinterval series often had the same fractional number of degrees of freedom (i.e., chaotic dimensions), a finding which suggests they are both regulated by the same underlying system. The ischemia/anoxia evoked transient dimensional increases and separations between the two subinterval series that, after the temporary divergence, reconverged to having the same lower value. The dimensional fluctuations occurred repeatedly and preceded or coincided with alterations in the magnitude and sign of the slope of QT vs RR-QT. We interpret the dimensional fluctuations of the two subinterval series as correlates of adaptation-dependent self-organization and reorganization in the underlying intrinsic cardiac nervous system during accumulating ischemia/anoxia. Such attempts at functional reorganization in this simple neurocardiac system may explain the transient dimensional changes in the RR intervals that precedes by 24 hrs the occurrences of fatal ventricular fibrillation in high-risk cardiac patients.     

Explanatory schema and the process of model building

Synthese - In this paper, we argue that rather than exclusively focusing on trying to determine if an idealized model fits a particular account of scientific explanation, philosophers of science...     

Lucky understanding without knowledge

Can one still have understanding in situations that involve the kind of epistemic luck that undermines knowledge? Kvanvig (The value of knowledge and the pursuit of understanding, 2003; in: Haddock A, Miller A, Pritchard D (eds) Epistemic value, 2009a; in: Haddock A, Miller A, Pritchard D (eds) Epistemic value, 2009b) says yes, Prichard (Grazer Philos Stud 77:325–339, 2008; in: O’Hear A (ed) Epistemology, 2009; in: Pritchard D, Millar A, Haddock A (eds) The nature and value of knowledge: three investigations, 2010) say sometimes, DePaul and Grimm (Philos Phenomenol Res 74:498–514, 2007) and Grimm (Br J Philos Sci 57:515–535, 2006; in: Bernecker S, Pritchard D (eds) The Routledge companion to epistemology, 2011), Kvanvig’s critics, say no. The cases put forth by Kvanvig’s critics share a common feature, which seems to drive the intuition that understanding can’t be lucky: the fact that the information that makes up the individual’s understanding comes exclusively from a bad source. I formulate a case that lacks this feature, drawing on the fact that understanding produced from scientific inquiry is often produced by collaboration. I argue that my case provides good evidence that understanding is not a species of knowledge.