## 4 Discussion
### Serial Measurements of DPOAEs \(\leq\)8 kHz  
DPOAEs elicited with standard parameters (L\({}_{1}\)/L\({}_{2}\) = 65/55 dB SPL; f\({}_{2}\)/f\({}_{1}\) = 1.22) at stimulus frequencies \(\leq\)8 kHz are routinely measured with clinical equipment as part of ototoxic monitoring protocols at baseline with subsequent outcomes compared to baseline results for the purpose of monitoring (reviewed by [5]). DPOAEs, commonly measured at a few points per octave (gross sweep), provide a generally frequency-specific snapshot of overall OHC function to assist with the determination of cochlear dysfunction during monitoring. Figure 5 (left panel) provides a clinical \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{4}{c}{**Summary of Results**} \\ \hline
**Paradigm Analysis** & \begin{tabular}{c} **Patients** \\ **Tested** \\ \end{tabular} & \
\begin{tabular}{c} **Patients with** \\ **Significant Change** \\ \end{tabular} &
\begin{tabular}{c} **Significant Change** \\ **Percentage** \\ \end{tabular} \\ \hline Gross Frequency Sweep & 12 & 1, 4, 6, 8, 9, 10, 16, 18 & 8/12 = 66\% \\ \hline Mid-Level Concentrated Sweep & 10 & 1, 4, 6, 8, 9, 10, 16, 18 & 8/10 = 80\% \\ \hline High-Level Concentrated Sweep & 12 & 1, 2, 4, 7, 8, 9, 10, 16, 18 & 9/12 = 75\% \\ \hline L\({}_{2}\) Fixed, L\({}_{1}\) Varied at Highest Frequency & 10 & 6, 7, 9, 10 & 4/10 = 40\% \\ \hline L\({}_{2}\) Fixed, L\({}_{1}\) Varied at 2 nd Highest Frequency & 9 & 6, 7, 8, 9, 16, 18 & 6/9 = 66\% \\ \hline L\({}_{1}\) Fixed, L\({}_{2}\) Varied at Highest Frequency & 10 & 8, 9, 10, 16, 18 & 5/10 = 50\% \\ \hline L\({}_{1}\) Fixed, L\({}_{2}\) Varied at 2 nd Highest Frequency & 10 & 4, 6, 7, 8, 9, 10, 12, 16, 18 & 9/10 = 90\% \\ \hline DP Level across Ratio at Highest Frequency & 9 & 4, 6, 7, 8, 9, 16, 18 & 7/9 = 78\% \\ \hline DP Level across Ratio at 2 nd Highest Frequency & 8 & 4, 6, 7, 8, 9, 10, 18 & 7/8 = 87\% \\ \hline Group Delays at Highest Frequency & 9 & 6, 7, 9/6, 7, 9 & 3/9 = 33\% \\ \hline Group Delays at 2 nd Highest Frequency & 8 & 4, 7, 18/7, 10, 18 & 3/8 = 37.5\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Analyses completed (n = 11), number of patients tested with each paradigm, number of patients with a defined significant change, and percentage of patients with significant change. case illustration of this \"clinical approach\" in a 55-year-old individual undergoing cisplatin therapy (100 mg/m\({}^{2}\) per dose) and concurrent radiation therapy to the head and neck (2 Gy per dose). Results in the left panel of Figure 5 illustrate DPOAE levels as a function of frequency (\(\leq\)8 kHz) across 3 trials (approximately 3 weeks apart) obtained on clinical OAE (Biologic Scout) equipment using traditional SPL calibration and standard stimulus parameters (L\({}_{1}\)/L\({}_{2}\) = 65/55 dB SPL; f\({}_{2}\)/f\({}_{1}\) = 1.22; f\({}_{2}\) = 1.5-10 kHz; 4 points per octave). DPOAE levels and average noise floor as a function of frequency (\(\leq\)8 kHz) across 3 trials in the right panel of Figure 5 reflects results obtained with research equipment [21; 39] using FPL calibration (see [18; 19; 20]). In each panel, the solid and long-dashed lines with symbols represent trials 1-3 with trial 1 noted as the \"baseline\" measurement prior to the start of treatment. The short-dashed lines without symbols denote the average noise floor across the trials. All DPOAE levels are displayed here for the patient; however, to be considered present for clinical monitoring purposes DPOAEs had to have an SNR of 6 dB, a level greater than \(-\)20 dB SPL, and have at least two adjacent data points meeting this criterion so not every data point has clinical utility for monitoring. At baseline (trial 1), the clinical approach yielded 3 data points compared to the research approach with 14 data points at frequencies up to 3 kHz for monitoring. The absent responses at higher frequencies are consistent with the pre-existing high-frequency, age-related hearing loss in both ears at trial 1.