muscle {MASS} | R Documentation

## Effect of Calcium Chloride on Muscle Contraction in Rat Hearts

### Description

The purpose of this experiment was to assess the influence of calcium in solution on the contraction of heart muscle in rats. The left auricle of 21 rat hearts was isolated and on several occasions a constant-length strip of tissue was electrically stimulated and dipped into various concentrations of calcium chloride solution, after which the shortening of the strip was accurately measured as the response.

### Usage

    data(muscle)

### Format

This data frame contains the following columns:

`Strip`
  which heart muscle strip was used?
`Conc`
  concentration of calcium chloride solution, in multiples of 2.2 mM.
`Length`
  the change in length (shortening) of the strip, (allegedly) in mm.

### Source

Linder, A., Chakravarti, I. M. and Vuagnat, P. (1964) Fitting asymptotic regression curves with different asymptotes. In Contributions to Statistics. Presented to Professor P. C. Mahalanobis on the occasion of his 70th birthday, ed. C. R. Rao, pp. 221–228. Oxford: Pergamon Press.

### References

Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S. Fourth Edition. Springer.

### Examples

    library(nls)
    A <- model.matrix(~ Strip - 1, data=muscle)
    rats.nls1 <- nls(log(Length) ~ cbind(A, rho^Conc),
       data = muscle, start = c(rho=0.1), algorithm="plinear")
    B <- coef(rats.nls1)
    B

    st <- list(alpha = B[2:22], beta = B[23], rho = B[1])
    (rats.nls2 <- nls(log(Length) ~ alpha[Strip] + beta*rho^Conc,
                      data = muscle, start = st))

    attach(muscle)
    Muscle <- expand.grid(Conc = sort(unique(Conc)),
                         Strip = levels(Strip))
    Muscle$Yhat <- predict(rats.nls2, Muscle)
    Muscle <- cbind(Muscle, logLength = rep(as.numeric(NA), 126))
    ind <- match(paste(Strip, Conc),
                paste(Muscle$Strip, Muscle$Conc))
    Muscle$logLength[ind] <- log(Length)
    detach()

    require(lattice)
    xyplot(Yhat ~ Conc | Strip, Muscle, as.table = TRUE,
       ylim = range(c(Muscle$Yhat, Muscle$logLength), na.rm = TRUE),
       subscripts = TRUE, xlab = "Calcium Chloride concentration (mM)",
       ylab = "log(Length in mm)", panel =
       function(x, y, subscripts, ...) {
          lines(spline(x, y))
          panel.xyplot(x, Muscle$logLength[subscripts], ...)
       })

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